Yes, go to Fred the Mindflayer in House Jorasco. You get one free feat swap after doing the Dragonmark quest in the Marketplace; after that it costs (a lot).
One other advantage to high INT on a rogue (apart from the extra skill points) is it boosts the DC on the Assassinate ability.
Yes - pretty much every melee (or ranged) build should take Imp Crit in its preferred weapon type ASAP, IMHO.
"PrE" stands for Prestige Enhancement. If you're familiar with PnP D&D 3.x (or other D&D CRPGs like NWN), they're similar to prestige classes, only they're enhancements (duh), not separate classes. Several classes have PrEs become available at class lvl 6; some PrEs get a 2nd or 3rd tier to them at lvls 12 & 18, respectively. Rogues have three to choose from: Acrobat, Assassin, and Mechanic. Read the
compendium entry to get the gist of each. Since nobody recommends making a minmaxed trapmonkey, nobody recommends Mechanic; that leaves Acrobat or Assassin.
The PrE(s) for your class(es) will show up in the builder automatically once you have the pre-reqs; or click the "Show Unavailable" checkbox in the Enhancements section.
Listen is a redundant skill, as Spot usually works just as well for finding stealthed creatures; and Spot is also useful for finding traps & secret doors. AFAIK the only thing Listen is good for which Spot is not is for hearing invisible creatures; and there aren't enough invisible monsters to be worth the skill points in Listen when there are more useful skills, IMHO.
OTOH, if you're going for a stealth build, I would max Hide & MS; just because players usually skip the Listen skill doesn't mean the monsters do too! :-)