Lua coding in relation to Halflife 2 modding

Would first learning some LUA help to get experience on how to get to grips with and create a fullblown multiplayer halflife 2 mod using the SDK?

I think you’d be better off with a real programming language if you already know any other language. If not, then Lua is a good start for it’s easy syntax.

Lua won’t magically teach you everything you need to know to create a HL2 mod. GMod modding is a good start, though. Once you become proficient at it, modding HL2 will become easier. Most if not all concepts that can be applied to GMod also apply to Source SDK, and the functions implemented in GMod are pretty much the same in HL2’s code. You will, of course, have to learn C++ and the more low-level concepts before starting a serious HL2 mod.