Just have a look at the assembly guide. From my head, you need 3x17mm, 3x21mm plain pins for wheels and buggies, and 2x22mm pins with notched head for tracks.
I'm not sure how servos would work with TK7.1 channels CH3 & CH4 (main power). You might need to use the HK gearbox with it (probably could fit with some model modifications).Also what electronics you use on your build?
I found the servos on aliexpress
I intend to buy a heng long 7.1 board and remote
Also, TK7.1 got pretty limited tank sounds, and you can't update it.
I'm using OpenPanzer RC, ordered it from PCPway to manufacture OpenPanzer_RC_Tank_Control_Board