Hi turbopimp187
The trucks are selfmade. But there are a lot of sources in the www to learn about "How to made you own tttt"
To build a 4wheeler is easier than a 6wheeler. So I suggest you to start with souch a rearaxle powered 4wheeler.
Military or not is a question of your mind. I prefer a civil truck like a Mercedes Benz Unimog or an old Iveco (a little offroad is my favorite).
Spring suspension is a "nice to have" but it isnt nessesary. It is good to have a moving frontaxle so all wheels stay on the floor (even by driving offroad). Springs looking very cool, but their bring much problems in.
best regards
Thorsten
www.mikromodell.de