I generally use the same-length cable for the corresponding speaker pair, like Left/Right, Surround Left/Right, etc. I don't think it matters all that much since Audyssey will set up your delays accordingly.
As far as cables, there is a thread on how to make your own cables. You can also buy ready-made cables from Monoprice, Parts Express, or Blue Jeans Cable.
You can terminate with Monoprice banana plugs, but I think Nakamichi or GLS Audio bananas are better quality.
I don't have Infinity speakers, so I cannot comment on them. As a general rule, I usually recommend using a similar driver configuration for the Left/Center/Right speakers. Looks like the PC351 is the best option you have with the P363 even though it is .75, 3.0, 5.25 vs. .75, 4.0, 6.5.
I have a 5308ci. Beauty of the 3808ci is that you can add an external amp if you need more power.
HD-DVD = 94
Blu-Ray = 120 ( 24 Warner red2blu )