Rather than using a crossbow to back up your spells, I'd recommend instead that you look at throwing flasks of acid, alchemist's fire, and holy water, plus other items depending on the setting and what you have access to. Splash weapons hit as touch attacks like spells, and you don't need Rapid Reload to make multiple attacks with them. You do need Quick Draw, but it's a more generally-useful feat than Raid Reload. Throwing them two-handed with other feats to get multiple attacks, you can even do more damage than with spells.
At the moment, you're putting all your feats into the utility side of your character. I'll suggest some feats for the combat side. For potion-throwing, you need Quick Draw. You may want TWF and ITWF for extra attacks. Given your feat limitations, the
gloves of the balanced hand (MIC 105) can get you TWF or ITWF. The other important ranged combat feats are Precise Shot, since unless your party is all ranged you'll probably be shooting at targets in melee, and Rapid Shot. You need Point Blank Shot as a prerequisite even though it's not very good. Far Shot might be worth considering if you expect you'll ever need to attack beyond 30'---use
sniper's shot (SC 194, CAd 157) to remove the 30' cap---though you can get it without spending a feat from a
helm of the hunter (MIC) or
horizon goggles (CM). Improved Precise Shot is an excellent feat but you'll never have the BAB to take it. Craven is also an excellent feat for sneak attack damage. Beyond that, Improved Initiative is good for everyone, and Extend Spell is good for all casters. I question whether Master Spellthief is worthwhile given how many feats you could use: all it gets you is +1 caster level, the ability to steal higher-level spells, and the ability to cast in light armor, none of which are enormously useful. The wizard variant that trades Scribe Scroll and metamagic/item creation feats for fighter feats (UA/SRD) can help getting the feats you need, and you'll want
heroics (SC) too.
Since you're relying so much on sneak attack, you'll want the ability to damage undead at minimum. I would strongly consider taking enough of unseen seer to get advanced learning for
grave strike (SC, CAd). Most of the other standard methods won't work for this character. Because you can't take Improved Precise Shot, you may also want some way of defeating concealment if your DM will use that to prevent you from sneak attacking, probably a
crystal mask of visual insight (MIC 92, CP 109) but see also
http://www.minmaxboards.com/index.php?topic=10479.0.
