This definitely sparks my interest... I don't have any experience making complex high-level characters, but I have always wanted to play a powerful character, so I'll have to keep an eye on this for when I'm caught up on my current games.
A succubus was my first thought for a character, but dragons are always tempting, and I have always wanted to play a nymph... though I wonder if this might not be the best game for that.
Well, succubus is 6 HD and +6 LA so they fit perfectly and they get many nice spell-alike abilities. With high charisma one the gestalt paths should make use from it. Nymph is 6 HD + 7 LA creature, so sadly nymphs do not fit in unless using a template which reduces your LA
Or wait, some members in party are 13th level and if other players do not mind, you could play nymph but when you get level up you do not get any monster stuff upgrades (not yet anyways).
Anycase key question to ask 'can I play this char in this game' is to tell me what you want from game? Want play powerful char? Sure, no problem, you can do exactly
that in this game :). But if your new to higher levels of play (we speak epic as your chars are CR 30 with gestalt + paragon creature template add), Kunoichi and others who are already in the game can give advices or discuss things in PM's with you if you so desire.
...you know what, I think I'm just going to go with an Anthropomorphic Giant Squid (3HD, +1 LA), then stack a big juicy template on top of it. It's basically a mini-Kraken without the weather themed SLA's, so I get everything I want in a much smaller package. Problem solved!
Sounds cool to me, just remember 1 inherited and 1 gained template max (half-dragon or half-fiend would work as inherited template which adds nice bonus to Str). Only exception are stacking sort templates (like evolved undead from libri mortis and I technically allow that template for outsiders as well albeit it's unfinnished house rule).