1) Each 'part' has it's own effect section, so no effect drop. You get a delay / reverb / chorus / distortion / phaser / eq / freq shift / vocoder / character per part.
2) You can do it anyway you'd like, but if you so choose the analog outputs remember you'll need to compensate for latency of the 'Virus Control' plugin, and others.
3) USB audio does lack a bit compared to the analog outputs, but when you throw everything into a mix it's quite hard to hear, IMO.
To be honest, I've never had the TI crash on me. I feel sorry for everyone who is having problems. Only thing I've had problems with is the delay sync dropping out sometimes, but it's not a huge deal. I use Cubase 5, as well, with a much lower spec machine as yours (3 year old core2duo laptop on XP). If you can get around that 64 bit problem which I have no experience with, then it's a very nice investment. I have a nice budget to invest in more synths/software but I can't come to spending anymore money cause I feel this machine does everything I can dream of already. Get a TI, NI FM8, and Minimonsta in a mix and you're good!
Goodluck