Fairly new into FPV and this is off topic...mostly. If not allowed, please delete. Quick info, I'm an airline pilot, have my own small Cessna, have always loved RC airplanes and getting into FPV drones a bit. This is more about electronics. Looking to build a small Thermal camera unit that I can mount onto the wing to help see when low to the ground, night, low vis weather etc. Yeah that's mostly easy. Here is what I want to do also with it. Have an OSD with full instruments as a backup in the cockpit. Oh, and it has to be wireless. (Can't be hard wired into the plane legally) So here is what I need or think I need.

-Thermal Camera (for now, going to buy a cheap camera for proof of concept)
-Standalone OSD (don't need a flight controller but if its all in one and that's easier than cool) Just want Artificial Horizon, airspeed, altitude, heading
-FPV transmitter (only needs to go max 20 feet to cockpit but want low latency and decent resolution)
-Pitot Tube (Digital airspeed sensor)
-GPS and Compass module (for heading info)
-Barometer (altitude) 
-Video Receiver 
-Video Screen (4inch or so and usb powered)
-Battery (would like it to last maybe 4 hours between charges)

All of this needs to have a decently wide temperature range to operate safely.  Bonus, but not required now, would be a paddle wheel that moves in the airflow to turn a little generator to charge the battery when flying or solar cell to charge when not flying. 

Okay, Ill take all the suggestions and help I can get! Specifics would be nice but I'm fairly new to this stuff. Be gentle. 
-E

Easy to do if you add in a iNav compatible flight controller with built in OSD.

The solar or paddle wheel charging is something that needs to be researched as I am unaware how compact and efficient this can be made to provide charge for the lipo.

An FC+GPS module+Camera+VTX do not use much current and can run very very efficiently but we will need to estimate total amp draw and size the lipo accordingly.

What are your budget constraints? I would say even with premium components from the hobby this should be doable under $300. If you go super budget then perhaps $200.

I am not sure how much a thermal camera will cost but you will need one with analog output that can run on 5v and not draw excessive Amps.

Look at OpenHD. There are several thermal cameras supported, and just requires a Raspberry Pi:
https://openhd.gitbook.io/open-hd/hardware/cameras

$300 is well within the budget minus the camera.

The reason I didn’t think of recommending OpenHD is because directly connecting GPS, Barometer, Compass, Airspeed sensor, Gyroscope to a Pi is going to be clunky.

Most implementations of OpenHD depend on Mavlink data from the FC.

This can be done directly with a Pi without an FC but I am not completely sure all the code required exists.

Furthermore you need two Pi’s and the specific wifi dongles required are not easy to source.

At 20ft distance to the cockpit, analog video quality is good enough to give you good video quality enough for display on a 4” or even a 7” display with an analog video receiver built in. This will make the setup alot cheaper compared to OpenHD.

One other thing I wish to add is that OpenHD hardware is not built to take a bashing like the stuff we use on our quads.