About soundcards, the best resource is here: http://www.alsa-project.org/main/index.php/Matrix:Main
Just pick up one from that list that suit your needs.
I have seen a Julia from ESI-PRO working nicely, but the support is still unofficial. I think a good card with the features you are looking for are the provided by M-audio. The Delta66 looks good: http://www.m-audio.com/products/en_us/Delta66.html
and appears in the matrix.
The Audiophile is also supported and may suit your needs, it is smaller: http://www.m-audio.com/products/en_us/Audiophile2496.html
About 64bits, you only would gain performance during encoding, I am not that anxious xD. Keep in mind that real time digitalization is done by the audio card Digital/Analogic converters, so not real gain at recording time, at least you use real time plugins.
A 32 bit kernel can use more than 4gigs of ram using PAE