Hey X,
yes you can do everything you want to do, you just have to combine the elements of the various mods you want into 1 mod.
for example, if you want a tank from mod 1
and a cannon from mod 2
you can create mod 3, with both the tank and gun in it....(you put the tank & gun in this one yourself)
how to do this, can be as simple as cutting and pasting entries in files...or as hard as getting free advice from a lawyer, it will just matter how complicated you want to go, what you want to do in other words.
Look at the tutorials, and BE SURE TO BACKUP EVERYTHING you might ever think about changing, and change only 1 thing at a time, test it in game to make sure it works, BEFORE going to make the 2nd change.