Foley.
I just finished a couple of projects with involving foley, probably about 20 hours worth. What I was told you need to do it properly (from a Foley artist that has worked on just about everything):
1) Direct microphone for the sound (shotgun!!)
2) Room Microphone (LDC)
3) Quiet room that you can vary the amount of diffusion
4) Lots of props
With a good shotgun microphone you shouldn't have any problems getting rid of any room tones that occur. If your ambient noise in the room is too much you could try some noise-reducing plug-ins.
I found getting good clothes sounds was to take some cloth in my hand, and rub it together as the character moves.
IMHO, leave the sound libraries for the SFX guys, and try and create as much stuff as possible. It's half the fun. The Sound Effects sounds very muffled to my ears (like an old cassette tape).
LAYER!! Layer everything, it makes for huge sounds, and you can always take them out later.