My first trans temp gauge took temp from the pan - I used a pan drain plug “kit” and then installed a sensor instead of a plug. Mounted the gauge on the A pillar.
For remote filter and cooler - here is a FWD set-up on one of the Volvos. Fluid goes from Trans > radiator cooler > thermostat (which routes it to an external cooler if hot, and bypasses if not) > filter>trans. Logic is this: cold fluid gets warmed more quickly by the radiator. Once warmed up - the 180F thermostat will route the fluid to the external cooler and keep the temp about there. The cars are operated in very cold climates, so, wanted temp control, not just a ton of cooling. That Volvo, by the way, is in Northern Vermont, sees extreme cold and wide temperature swings. The fluid flows even when it’s -20F. It has AMSOIL fluid in it.
I used a Baldwin filter. B2-HPG, which has a built in bypass valve.
Baldwin spin-on lube filters protect your engine from wear particles that can otherwise lead to premature parts failure.
ph.baldwinfilters.com
Derale makes a variety of mounts, and I used a Derale thermostat. I used a B&M 70264 cooler. I prefer the stacked plate to the fin & tube. More impact resistant (small rocks, etc.) and greater heat capacity. You could easily plumb a temp sensor in the lines.
For fabrication - I really like the “nut-sert” nut inserts, they work like a pop-rivet, and allow a thread nut in a blind hole. For clamps, Oetiker stainless steel band clamps. Quick to install, don’t leak, cheap. You have to buy the crimp pliers which are not cheap, but the clamps are cheap and the system works great. I’ve done this set-up on four cars. No leaks. No issues.