Welcome to the AFV again...
Here some replies , which I hope can help you a little:
1. Is a "filter" the same thing as what used to be called a "wash"?
--NO, is different, but during lng time for many people was the same. You can read more about both technics in an article that I write here long time ago:
2. How do I pastels? Are they smeared on or are they dissoluted with a little water? I have the Tamiya weathering pastel set but have no clue how they are to be used (and while excercise brings skill, I do not feel like wasting the first tanks I do - wouldn't be very encouraging, would it?).
--The Tamiya pastel is a little different that the pigments used actually. I recomend you to use the tamiya pastels directly, without any other product added. The Tamiya pastels is mixed with wax, and it is helper to fix the powder, but is not good combination for water or other products, because the structure is oily, and it don't work well with water. If you want to work with water or other liquids try modelling pigments.
again, here you will find another article about it:
Anyway, I recomend you to try even with the first tank...because is the only way to learn.
3. When you spray earth over the wheels and tracks, do you do this before or after the roadwheels and/or tracks have been fitted? Do you thin the paint a lot?
--BOTH methods is good. Separatly wheels or tracks is easier and more accurate because you can work with more detail (the weathering...dust, mud, metal, rust or rubber), but if you have glued the wheels or tracks to your model, you can work over it anyway. Sometimes to glue the wheels is totally necesary, but if you can choose, left the wheels separatly....
4. I know that this is the worst question of all: How do I paint the tracks?
--DO you means with brush or airbrush?? or muddy or rusty?? dusty or clean? wich colors? wich methods or technics?? acrylics or enamels??? (depending of the tracks: plastic or metal or rubber). Try to explain better thequestions, giving us more detail about how is your tracks and how is the terrrain where they are running...
I hope it can help..good luck and ask us if you have more doubts..