Starting a list was a good idea. You can never have too many options at your fingertips.
As for actually making film, I count the substrate part of the process as a solved non-issue. Dupont doesn't sell to the public, but 3M does. 3M 9960 and 3M 9962 are excellent products. 9960 is 6.8 mil polyester, coated on both sides with a hydrophilic subbing, and the perfect thickness for sheet film. 9962 is 3.9 mil and perfect for roll film. The places I talked with that carry it do have a minimum order, but as these things go, it's reasonable. I ended up buying mine from Custom Converting, Inc. in Oceanside, CA, but there are a couple of places on the US east coast, too. I spent $1200, but I have enough film for a lifetime! Interested people who don't really need a lifetime supply of fim could organize a group purchase.
Really, seriously, unless soup-to-nuts DIY is important to you, go with subbed film, at least for now. It will let you concentrate on learning to make great emulsions (although zapping film does sound kinda fun.)
Steve: No worries! Thanks for the thought.
Jason: I didn't have much luck with Dura-Lar or kin, and I think I tried every surface Graphix makes.