Never done 3D painting but I´ve painted several logos on the skirt vents and hood of the GT3R. Yeah, takes about a days worth of dedicated work but it can be done. I don´t have photoshop and won´t be able to afford a current version, so GIMP it is. Maybe 3D is possible there too, don´t actually know.
This might take two days (16h) to place some logos in 2D but you can still make yourself believe that it´s all fun.
Looking good!
You can pay for a subscription to Photoshop through Creative Cloud for 1 month - IIRC it's $20USD for the month for one program, and $50/mo for the entire Creative Cloud Suite. Makes things a lot more palatable for hobbyists and freelancers. And that will be the full-featured, full-balls completely legal program.