Welcome to the Forums Astral. There are lots of great guys, and gals, on here that are very knowledgeable and are ready, willing and able to help you with your questions and/or problems. Don't be afraid to go to the specific Forums with your questions. The people here don't bite. I'm not an expert on all these questions but I'll try to help you with some of them.
These new kits can be a little scary at first, but, as you get used to working with them, it will get easier. To answer your first question, an airbrush is not a must. There are lots of people on here that do not have an airbrush and only use rattle cans or the old standby the brush. I used rattle cans and brushes up until a few years ago. I'm just starting to get the feel of my airbrush and learning how to use it properly. It takes time.
On weathering. Start small with things like powder burns on the wings from the machine guns and exhaust smoke on the fuselage. Start with small things like these and work your way up to more complicated items. Slow and easy does it. You can always add more but it's hard to remove too much.
I'm not sure about your paint question. I think it means to mix the colors and then apply, but don't take my word for it. Go to the Paint Forum and ask that question. Someone there will help you that knows more than me.
There's no such thing as a stupid question. The way to learn is to ask. Hang in there and keep at it. Good Luck.
Jim
Main WIP:
On the Bench: Artesania Latina (aka) Artists in the Latrine 1/75 Bluenose II
I keep hitting "escape", but I'm still here.