That's about the best advice you can get without people telling you exactly which parts to get imo.
Just 1 remark:
1 graphicscard > P55
2 or more cards > X58
In other words, an i7 will run fine on P55.
* I lied! You don't get triple channel with P55.
Still, P55 isn't a good choice for SLI/Crossfire.