I am really not sure if others can see you skin online because I have GTR2 only since 3 days now, but I think the answer is: yes. I'm a GTR2 noob, my first GTR2 skin. (Not my first skin ever, have done some for F1 Challenge ETCC Mod and GTR, but never raced them online)
about templates: there are templates on gtr4u.de. And there are some good tutorials on rscnet about how to edit the files. I've read them and they really helped me, and it would take a lot of time to explain everything detailed. Look at the sticky topics in GTR2 and GTR section.
I have 'painted' the skins with Paint Shop Pro, but if you can handle Photoshop, you have much more possibilities.
Your cars will be ready, ehm, I'm not sure when, maybe tonight but probably tomorrow.