I think Scott addressed the first part of your post above.
If I rip a model from a video game and use the templates that I create from the gaming model and build a physical model of the thing, am I breaching some form of copyright?
This part.... :facepalm
Lots of questions lately about copyright law. Seriously, if you reproduce any copyrighted thing, without obtaining proper permission to do so, you may be subjecting yourself to risk. That risk is usually (Read that word) directly proportional to the amount of money that you make in distributing said thing.
So if you make a one off for youself,
USUALLY no problem. Maybe not really legal but not an issue.
You make 7 of said item and sell them for the basically cost of parts to a few really dedicated fans, again usually not a big deal. and you may get a nod from the creator (not the copyright owner) for being a cool fan.
You decide to mass market said product and hope to make a mint, get ready for lawyer time.
That generally is going to apply reproductions of props, out of print model parts, 3d representations of models created for a studio released game/movie, whatever.
If you don'd have the rights to reproduce it, and it is copyrighted, you don't have the rights to reproduce it. End of discussion.