Alright, first question I have so far: I'm starting out with using Blender to make game models, and I was wondering if I needed to make things to scale, or if models are supposed to be scaled down in the game? I was curious because I noticed that so far the mp5 I was modeling is much bigger than the army truck I'm making.

The model's you have created in Blender can be scalled down in the game engine you are using. If you are using Blender as your game engine then I think you can either scale them down with the S key OR script it to scale the model down to what you want.