I have an idea for a small mod I would like to try creating at some point. The concept could be implemented as a content-only mod, but with limitations. As far as I'm aware, the Source source code is available somewhere, and can be modified. I've done the occasional small project in C#, but I'm by no means a full-time coder, so my question is this:
Can a mod (I understand Source Base 2013 is usually used for such purposes?) be created from modified Source 'just like that', or does it require licensing from Valve? (Assuming you'd still need HL2/EP2/S2013 to run it)
Is adding one entity, a keybind, and a HUD overlay something that'll take a lot of effort or something that is manageable with some pre-existing programming skills and a lot of googling?
Cheers and thanks for any and all advice <3