If you're recording vinyl to hard disk, then latency is not an issue -
it's only relevant to multitrack synchronisation. The question you
need to ask is - how many simultaneous inputs do I need? If you're
recording solo material, building up one mono track or a stereo track
at a time, then a stereo card would be fine. You only really need
more inputs if you have a live band.
The M Audio Audiophile (PCI version, not the USB) would do a good job
of both your vinyl transfers and your music recording.
even though Audacity can mix multiple tracks, this is
not it's
primary use. It's more of an editor.
I'd disagree completely - the Audacity interface is totally designed
for multitracking. If you just want an editor for a stereo file,
Sweep or Glame is designed for that. There's also gramofile and gwc
specifically for doing vinyl clean-up.
You might want to consider
something like Ardour.
I personally am looking forward to using Ardour, but recommending it
as a starting point - you've got to be kidding...
Cheers
Daniel