Will I need more than just one Source game?

This is a pretty dumb question, but I’m rather short on cash and can afford GMOD and one Source game, HL2/Ep1/Ep2. If I want to use models or maps or weapons from, say, CS:S or TF2, would I need to buy those too?

Again, obviously a yes/no question, but all I can find with my arbitrary Google search is “You need at least one to play GMOD at all.”

Now, if the answer is yes, that I do need to buy more to make use of maps and models, is it possible to shadily track down the data I need (exclusively for Gmod use) from an external source.

tl;dr do I need TF2/whatever to use TF2/whatever models in GMod and if not can I just download them for the express purpose of using them specifically for GMod without getting myself banned from Steam or something?

EDIT: Never mind, a more refined search got me my answer (which is unfortunately ‘Yes’.) Any mods/admins that happen to come across this are free to delete it, I’m done.