Well, first of all, the Undead Lord archetype isn't really worth it unless you have a lot of downtime between adventures, and a large menagerie from which to draw bodies for your undead companion. If you want to stick with Cleric, I'd suggest avoiding the archetype unless you really really want the companion. It's widely seen as a trap choice.
I personally love the Agent of the Grave, one of the best five level prestige classes imo. My advice would actually be to go Juju Oracle instead of Cleric, this not only reduces MAD, but also gives you the lovely Juju zombies (Seriously, read the template) and 6 HD of undead using Animate Dead instead of the usual 4. Then just scour the other spell lists for some non-Oracle spells, and have enough Int by lvl 5 Agent to grab the ones you want. Oh, and if you get a Trait for your character, make sure to grab Magical Knack so you don't lose the CL from the Agent.
For feats you'd likely need to get Spell Focus and Greater Spell Focus in Necromancy, I'd also suggest Undead Master if you're gonna be heavily minion focused. Spell Specialization and Spell Perfection in Animate Dead is just awesome, I'd suggest your three Metamagic feats be Extend, Heighten, and Quicken. Also, if you can afford it, consider getting Varisian Tattooo in Necromancy. As a last note, if you're going to be LE or CE and want to use Summon Monster spells for undead creatures, you'll want to get the Sacred Summons feat.
For basic undead minions nothing beats Juju Zombies, really, the template is crazy. If you just wanna get some skelingtons, you'll always want to get Bloody ones, and having a few low HD Burning ones is really great too (They're basically walking, flaming landmines)
The only really good magic item I can think of for a necromancer would be the Darkskull, so you might want to grab one of those. Otherwise you're pretty much free to get whatever magic items you feel like, though obviously a +Cha item is a priority if you're going Juju/Agent. Getting a small +Int item might not be bad either, just make sure that you've been carrying it around for at least 24 hours before you get to lvl 5 in the PrC
This is just off the top of my head, I have a family holiday thing to go to so if there's anything you want expanded upon please feel free to tell me and I'll get back to you once I'm home.
