T-Rex,
First of all, hats off to you for trying to build your models and enjoying the hobby.
Kettenkrad (spelling?) did have trailer and I've seen some photos of it carrying jerry cans and ammo boxes. Not sure if it did hauled any 88mm shells for tigers. You should be able to find enough photos of it on the web.
Think about where you want to be and what you want to do in this hobby. If you are just enjoying this hobby for your own satisfaction, then you should do whatever is pleasing you (that also includes painting your models with wall paints). However, it seems like you are aiming to go for competitions and that will require you a lot more work, effort, time and money.
As many of us informed you (based on your comments and your request) that you should invest little time into doing some basic research of your own and invest little money into basic modeling guides and books (or if you have access to local libraries or bookstores, spend some time at these places). I spend hours at my local library and guess what? These public libraries have a WHOLE section dedicated to WWII subjects (as well as most conflicts). Lots of books, photos and even magazines that are specific to WWII.
I also have Badger 350 airbrush and I've been using Tamiya paints and MM Enamels. I thinned both of them (I use Tamiya paint thinner for Tamiya paints and Lacquer thinner for my Enamels). I haven't had any issues with it. If you are using arcrylic paints, don't let it sit in open too long.
Just like any other hobbies (my scuba gear set cost me about $1400, but to refill the air in the tank, annual inspection of my gear and cost of dives are even more) the cheapest and easiest part of this hobby is purchasing kits. Everything else on top of that (books, paints, supplies, add-ons like photo etched parts, detailed sets.....) is really going to cost you an arm and a leg. Invest a little at a time (you don't need to have fancy tools to make great looking models) and invest some time into your hobby as well. In a long run, it will help you to move up to the next level.