New build for Newbie

[Canman172]

Hello all,
I am new to the RC world but I am experienced with electronics and ROVs.
I am starting a build of a 4WD non-steerable RC inspection crawler for internal inspection of pipelines.
I have been researching parts for my build and I would like to know if anybody can offer assistance especially in the control area.
I have compiled the list below of parts I plan to purchase;
4 x 12v DC planetary motors 100 RPM (5 amp stall)
1 x associated hardware for wheels
1 x Taranis X9D plus with receiver
2 x Motor controller boards (7 amp max)
1 x camera with Pan and tilt
1 x servo driver board
1 x FPV980 900 MHz 800Mw Plug & Play System for video transfer
2 x 4S 18,000mah batteries

All the above is going into a sealed 4" water tight tube which will be on wheels.
Is there anything else I need on the control side?
Can I control fwd/rev and the pan and tilt from the Taranis transmiter?
Final question.
I need to measure linear distance and have it on my video screen. How can I accomplish this using an encoder?
Sorry for the long rant. Thanks for your time.
Any drawings would be greatly appreciated.