i have yet to get a proper answer for this question. i think most people use a 2 axis gimbal. there is someone in here that has a 3 axis gimbal tho as they have the drone film its own arms moving from the down position to the up position.. good luck

Your website is a good web site. There are many useful information for us.

Loads of cameras,
I've been using a runcam split v2, excellent camera.

I've shelved mine to be honest I lost interest and started making foam planes. I'll get back to it at some point.

The problem with 4k fpv would be latency, for fpv you don't need crystal clear pictures if you've got a means to record from a decent camera and have a separate fpv camera then your getting the best of both worlds. I liked the idea of the split for it's quality of recorded video and the low latency of the built in fpv which is in itself a good picture.

For 4k fpv I'm not aware of any ready to go systems but doesn't mean there aren't any of course, a lot of people use a go pro to record and have a cheap fpv set up for lining the shots up.
I've read a lot of bad reports about the go pro video transmitting system but don't know how it works, Im thinking it works on WiFi which limits it somewhat in range but I also believe it has big latency issues.

If your ok with a separate fpv camera or guesitmating your shots somthing like the go pro wouldn't need wires.

The dji cameras are like the split, the bit on the gimbal is just the lens and image sensor, the actual electronics are built into the main boards. As far as I know no-one has interfaced with either their cameras or their gimbals. One day I might achieve the gimbal side but for now I'm going to stick with my split for the camera.

Keep us updated what you decide.