Getting my hands dirty in modelling

I’ve always wanted to piddle around with a source mod environment, so I did exactly that, I downloaded a copy of the source code on github and set it up in visual studio. Maybe one day this test environment may grow into something bigger, I don’t know. Anyways, on to the topic, I’d like to get my hands dirty in modelling, I mean, I’ve made simple props before, but I want to move on to actually editing the arms and hands model and vanilla hl2 weapons, just to see what I can come up with. How would I begin to go about editing the stock HEV arms and replacing the vanilla model with my edited version? Furthermore, could I apply the same techniques to weapons? I realize this may be a very broad question, since I’m really a texture artist/mapper at heart. But exploring the weapons code helped me understand the foundations of adding new weapons into the game. I managed to create a new pistol type and slap a CZ-52 model onto it from game banana, (only thing that failed was defining a new ammo type in item_ammo.cpp, but that’s a different story.) So, if any of the great modellers here on facepunch could help a novice like me, I would be most grateful! The software I like to use is Blender, by the way.