aircraft diorama - novice

You should be able to find figures and equipment at any hobby shop.

If looking on line shop around a few stores to find something you like, they don't always carry all the same items and prices may very also quantities in stock.

I was looking for some figures I wanted and spent several days looking for a vendor that had them in stock, ended up finding them at HLJ in Japan, the set of 4 was out of stock so I had to buy them individually, a week later the 4 pack was in stock again.

Different folks have developed assorted ways to do a surface ranging from poster board, sand paper, plaster or wall patching compound, celluclay, real dirt or a mix of them.

For building up areas blocks of foam or wood are normally used as a filler.

For foliage scale train supplies are normally used, things like static grass.

All this stuff is available on line and much of the base materials can be found at art and hardware stores.

The Model Railroad people cover these subjects. At the scales you speak of HO Gauge products will work for you. Suggest getting  info/books at your local library, used book stores for hard cover or magazines. Wargame figure hobbyists have their materials and techniques as well.

One pet peeve I have is do not use sand paper for street work, dust bunnies will get ya!

Art supply stores have products like acrylic mediums in different textures, Example "Liquitex"ceramic stucco texture gel #6416, try Michaels, but don't forget your coupon. Good luck and have fun.