Wow, it's looking good. You've created a lot of texture to the rust (perhaps a bit thick in places) but it looks good. The tire is absolutely beautiful and a great touch.
Here's a good discussion to have about these techniques:
Here's a bit of clarification on all these techniques.
Okay, so the idea is that FIRST you have to decide how rusty and gunky and gone do you want your vehicle. If you want to build a daily driver, then you know you have to NOT over do it. Now, for this build, Cranky went all out because Cranky LOVES, LOVES, LOVES rust and far-gone vehicles, but you already knew that.
Okay, so once you figure out how much rust your vehicle is going to have (it helps to have reference sources, pictures or look around in a junk yard, etc) then you prepare accordingly.
One little dent goes a long ways, two rust throughs go a long ways, etc . . .
So here are the basic approaches, or tricks in your bag.
#1) You can decide to paint your model, and then use the sponge technique to add rust spots sparingly with black and brown paint.
#2) You can chip and map the paint by using the TABLE & ROCK SALT Method. You can also sprinkle a bit of baking powder in a little bit of super glue strategically placed on the rust spot on your model and this will add texture (old technique, sure) but it still works. Or you can use pigment powders to do the same and affix them with a little thinned out matte medium or flow matte medium.
#3) You can buy insurance on whatever rust you want to add by simply airbrushing a few coats of hairspray on the body (over the rust coat) and then using a stiff brush and warm water you can chip away at the paint.
You can practice each of these individually and then you can begin to combine them always experimenting to achieve a higher level of realism in your work.
After all, this is exactly what military modelers have been doing for years now, getting great results. I just want to make sure everyone understands that these techniques are also available to us model car builders . . .