The only caveat I have with allowing rolled stats is that with a higher player power level, the threats you face will have to be altered to match. Keep in mind that monsters do not have ludicrously high AC even at higher challenge rating levels (balanced against 'an appropriately-equipped and well-rested party of four adventurers'); a Fire Giant has an AC 18 (challenge rating 9), and an Adult Red Dragon (CR 19) has an AC of 19, and an Ancient Red Dragon (CR 24), has an AC of 22.
Even a first level character with 12 strength can swing a sword and hit most monsters on a good day, though with somewhat less effectiveness and prospects on survivability. Most monsters get by based on alternative defenses or a really good offense.
In short, the game assumes you start with one or two moderately high stats (15-17), a couple of above-average stats (12-14), and a couple lower stats (8-11). You don't need to max out your stats to be highly effective. If you want your stats to be higher, you're assuming you need fewer stat boosts, and thus can afford more feats, and thus are assuming a somewhat higher powered game.
Regarding level, I think level three is a good place to start for this. Things can still start simply enough, and you'll be challenged, but you've already got some experience under your belt. Level 4 won't be too far ahead, relatively speaking, and should give you something to look forward to. More-so, despite the generally slow pace of PbP, it'll give everyone a taste of what play is like at early levels and onward.
For equipment, assume you start with whatever mundane equipment you expect to adventure with, and an additional 200 gp. You may also start with two potions of healing (you can swap one or both out with a potion of climbing, which lets you auto-succeed on athletics checks to climb for 1 hour, or a potion of jumping, which triples your jump distance for 1 hour, or a Longstrider potion, which increases your speed by 10 ft. for 1 hour). Finally, you can select two magic items of uncommon rarity. You can alternately give up both of these to start with a single magic item that is somewhat more powerful and more closely tailored to your character. It might be an heirloom handed down through generations, or perhaps something your character stole that was beyond their understanding, etc. This is, of course, an option for adding a bit more depth to your character background, and is thus ripe with fodder for DM meddling.
re: spending money on rituals; Sounds fine to me, though you still can only cast rituals of a level you can cast spells. You can spend regular money on a ritual scroll, which will allow you to transcribe the ritual into your Book of Shadows, or you can give up one of your uncommon magic items for two 2nd level ritual or three 1st-level rituals.
Also! If no one has a preference for campaign setting, I will pick one randomly. So far there's been only one suggestion, and it would require a bit of research on my part since I'm not fully familiar with Planescape as a setting.
Finally, I tend to reward well-thought-out characters and good roleplaying. Furthermore, I encourage creative uses of skills and ability checks. If you think doing something a specific way would be cool and can be reasonably performed with the resources at your disposal, even if it isn't strictly allowed by the rules, I may let it slide and very well might award Inspiration for doing so, or more.