Ability scores look good. As do feats. I think Sacred Geometry would have to be your 3rd level feat (requires 2 ranks of Knowledge Engineering), otherwise Craft Wondrous Item would be the strongest pick (since it breaks WBL in half). If your GM allows feat retraining to take multiple feats with a higher level requirement, perhaps you could get both. For traits, in hindsight, only Great Old Ones qualify for Worthless Pawn, not Outer Gods, so either change the religion trait or change the deity. However, Shub-Niggurath is the only deity that qualifies for Dreamed Secrets with the animal domain. A Separatist Cleric could get add the Animal Domain to any deity but your animal companion will be at -1 level (-2 if you prestige for a level). If you get the Beacon of Faith faith trait, depending on how the GM interprets it, that may give you an extra 2 levels of animal companion (up to a limit of your character level) and let you dip a level (or three if you're not separatist).
1) Charisma is a dump stat because the only thing it affects are your character's social skills and UMD, which is pretty negligible in the first place (except UMD - if you're determined to exploit it, it is hideously OP - but I guess that goes for social skills too) but with the right traits and/or feats you can pretty much make all that Int-based instead (Paizo has a hard-on for Wizards, you see.) at which point charisma is well and truly useless. And given how often GMs would rather have you roleplay social encounters instead of rolling skills, those social skills frequently might as well not even exist. And if you have Wis, taking a rank in Profession (Barrister) will let you argue your way out of tight spaces as well. Since a point buy or just dice rolls will leave you with some garbage low stat, Charisma is where low numbers go because charisma barely matters, unless you are a cha-based caster (in which case you max charisma).
On to the issue of channeling: Whenever you could channel, you could also cast a spell. Spells are better than channeling. This means combat channeling is bad, unless your spell selection is worse. In order to make combat channeling decent, you would have to take the Quick Channel and Selective Channeling feats so that you can channel as a move action (which does not compete with spells) and not hit the wrong targets with friendly fire. You can always just relegate yourself to out-of-combat healing with channel energy instead and invest zero feats. Since you channel negative energy, out of combat healing is not possible, but you can take Command Undead, which is actually better than casting a spell for CCing undead, provided you have a solid charisma to make a decent DC (and decent daily uses). Since your character has an absurdly high stat array, it would be possible to do this. However, once you get Dreamed Secrets you could also just cast the wizard spell Command Undead instead (this one only lets you target 1 undead, however).
Speaking of Dreamed Secrets, remember that it is possible when preparing spells to leave spells from the previous day, and with a Pearl of Power it is possible to restore an expended spell. For Dreamed Secrets this effectively gives you a way to prepare more than 2 wizard spells.
2) Melee is not really the route to take. You shouldn't attack with your standard action. But if you get a reach weapon and combat reflexes (hell even without combat reflexes you still get 1 attack of opportunity, so might as well make use of it with a reach weapon aka longspear) you basically collect free attacks during combat. However, if you choose not to use attacks, you can take advantage of a Tower Shield and Heavy Armor since the nonproficiency penalty to attacks and arcane spellfailure chance doesn't exactly mean anything when you're a divine caster. Take your pick. Alternatively you can get the Armor Training combat trait (and/or the Sargavan Guard region trait) to reduce armor check penalties by 1 then pick up a +1 Comfort Mithral Hellknight Plate at high levels (costs 17k gp) but if you have both traits you can pick up a regular Mithral Hellknight Plate (costs 11k gp, 12k if +1) and this way since your armor check penalty is zero the nonproficiency penalty does absolutely nothing while you still get to wear plate armor (and as mithral you still get the +2 AC bonus from 14 dex instead of +1). Forsaking attacks however is the easiest way to get a strong AC because a Full Plate and Tower Shield will only run you 1530 gp while you get 13+1 (dex bonus) AC for 24 total before any magic bonuses (26 if you burn 2k on a +1 shield and +1 plate). Otherwise you are looking at using a Four-mirror Armor (or breastplate if you want to spend 155 gp for -1 armor check penalty and -15 lb weight) for 18 AC until you can afford that mithral plate to bump it into 22 (21 if not +1).
3) Warcat of Rull seems to top out, however a Deinonychus or Velociraptor doesn't need the Narrow Frame feat for 5-foot squares and they have a charisma high enough to take Eldritch Heritage feats (better at 11th level), but their strength sucks. Alternatively you can get an ape, put an ability score increase in int, and deck him out in a bunch of weapon feats (so Weapon Proficiency (Longbow), Point-Blank Shot, Precise Shot, Rapid Shot). Remember you can always dismiss your animal companion and perform a 24-hour ritual to get a new animal companion as desired, for free.
4) Tark's prestige recommendations suck. There actually are a lot of strong prestige classes in Pathfinder, and for Clerics too, but if you have an animal companion you can only prestige one level without losing animal companion advancement (boon companion has a level left over) and when you stack Samsaran Mystic Past Life to steal another divine class's list and Dreamed Secrets to steal the Wizard list you kinda already have the good stuff without prestiging. Pathfinder Savant isn't worth the loss of a spellcaster level when you already have a massive spell selection, Veiled Illusionist doesn't do much either with Wizard spells at your disposal (Thematically it seems Sivanah should be your patron deity for it but the PrC itself has no such restriction afaict), etc. Exalted doesn't advance domains (inexplicably) and there is no Deific Obedience for your patron deity. Demoniac doesn't work either with your patron deity (and is really only worth it if you are building a level 13/16 character for fast Demonic Obedience boons, some of which are pretty sick).
If you go Neutral Evil you could pick up
Diabolist prestige class for 1 level (which is all you need) without losing animal companion levels and obtain an Imp Companion which scales off of your caster level on top of your animal companion. This is hands down the strongest option at your disposal, since the Imp Companion is a second animal companion, except on steroids. However, the imp companion is ultimately loyal to Hell so it might give you a spot of trouble with your campaign. I suppose you could also prestige into Green Faith Acolyte (which is weak until high levels - at 8th you get Wild Shape I and at 10th you get 10 extra spell levels to prepare - and you do get minor perks) since Shub-Niggurath has a strong nature theme and you lose only a few animal companion levels. Hell you can get both. I would use backstory to cover Diabolist's requirement or you can wait until 8th level to take it and cast a Planar Binding or Planar Ally at 7th.
If you're willing to lose more companion levels, Veiled Illusionist (gives you illusion spells, including Shadow evocation/conjuration, simulacrum, etc. I'd say, except you can cast the real deal because Dreamed Secrets hell you can cast the illusions too) and Soul Warden (Worthless Pawn lets you cast Consecrate and Dreamed Secrets lets you cast the Command Undead spell) are options I suppose. I'm not sure if Genie Binder is worth the loss of animal companion levels though.
Really there's nothing much good left for you (except Diabolist) since you already have access to damn near all the spells in the game short of bard-specific ones, depending on how you use Samsaran Mystic Past Life.
5) Support/Necro/Caster I suppose. Battle/Archer is dumb because you'd be burning standard/full-round actions on fighting instead of casting, and you already have a companion (or two) for this but I suppose you could do that if you cast Ancestral Gift for a martial weapon (with a decent bane property or seeking if it's a bow to negate firing into melee and soft cover penalties) and then maybe a Greater Magic Weapon on it and then in combat you cast Divine Power on yourself. Better yet you could get yourself an ape and/or imp and use Share Spells to give them the martial weapon with proficiency. I also don't recommend blaster casting as a Cleric (see: Wizard guides I linked above) - unless you get Dazing Spell metamagic because dazed is a disgusting OP condition.
