The Meaning of Life, the Universe, and Everything.
I wouldn't mind the alternate textures being provided in a separate file, as I have no problems using Photoshop at all. (To be honest, I was 1/3 way through making a 64x texture pack when I found PureBDCraft. I have since given up! I like it too much!)
However, I wouldn't mind seeing a customizer either. Perhaps something similar to the one that Rhodox uses on Painterly would be nice. (Before I went high-resolution, I was using Painterly.)
Your main priority should be finishing off alternative textures and mods you want to
support before any further adventures. I personally think MinecraftCustomizer is the best
resource you have at your disposal.
I honestly don't see the sense in creating your own website. While I don't doubt the
design will be awesome and it could probably suit the users' needs, it's not realistic
when considering the amount of time the creation of the site would take up.
Personally, I'd go:
1. Upload alternatives to MinecraftCustomizer.net (Not *such* a time consumer...)
2. Add additional Mod Support
3. Begin venturing for a new texture pack, Medieval pack seems more intriguing then
a possible future variant, but it's up to you.
My computer is a beast, 4.0 GHz Quad Core, 16 GB of RAM, and an overclocked to hell and back GTX 460. I can't even load the 512x when dedicating 8GB's of RAM to MC, I just get MC has run out of memory. Not practical IMO.
I'm of the opinion that if you really want to do a customizer, just use MinecraftCustomizer to save yourself some time. Unless, however, you really want to make a website.
Personally, I think you're fine just doing alternate png's for people to swap in themselves, but I realize customizers are growing increasingly popular and not everyone understands how to edit a terrain.png.