I'm currently in a cafe build myself. I would recommend making a plan for yourself. Get an idea of how you want it to look and perform. Price parts so you can get an idea of how obnoxious costs are going to be. Then start in.
It took me about 4 months to plan the build, 2 months of cosmetic changes, then i started in on the mechanical side. I'm about 1/2 through now (after 3 more months).
Seat pans: fiberglass or aluminum/steel. I personally gravitate towards fiberglass. It's pretty easy to work with if you want to try your hand at making your own. It's also light weight. I got mine from here:
http://www.airtech-streamlining.com/vintage/vintageseats_round.htmAluminum/steel will probably be more durable but can dent.
Parts suppliers:
I used dynoman for the big bore kit, valve train components, misc stuff
powersportsplus.com for OEM stuff
CMSNL.com for more OEM stuff
DavidsilverSpares.com
VintageConnections for electrical (regulator, rectifier, and harness rebuild)
That's as far as I've gotten so far.