Notes:

Most parts should print without supports (except cableJunction and motorMountA). Some larger parts can benefit from a small brim though, depending on your print setup.

I printed most structural parts with a wall thickness of 2mm and 1mm top/bottom to get the desired rigidity. This can be tweaked depending on your requirements and application.

Assembly

Use a good epoxy to join the parts that are printed in multiple parts. (Tip: leave one or both arms unglued for easier assembly)

The small pinion gears (SpurGearM1x16) work but not for very long, at least not in PLA. Forces on these are quite strong. They will get you going but metal versions of them can be had for extremely cheap from China/Ebay (search for M1T16 pinion gears).
I switched mine out after a while and it's been working very well ever since.

You'll also need:
4x 6000 Series deep groove ball bearings (OD 26mm ID 10mm Depth 8mm)
2x Nema17 stepper motors (mine are 17HS8401, 1.8A)
1x 10mm aluminium tube or similar metal shaft
2x proximity sensors M12 (optional, mine are LJ12A3-4-Z/BX)
The cable junction is proportioned to accept 3 mini XLR type sockets, if you decide to use this part.

A whole lot of screws of varying sizes. Next time I disassemble it I will make a list but I just used whatever I had on hand for mine. They are mostly 2.5mm and 3mm self threading screws of various lengths.

Let me know if I forgot to mention anything else.

Oh, it's designed to fit my D3400 with cables sticking out. I don't have a full frame camera so am not sure what other models will fit on it. Let me know if your camera fits and what model it is.

Enjoy! And let me know if you do anything cool with it.

One last note

I am controlling my gimbal with g-code, Grbl 0,9, a Raspberry Pi and a set of cheap noname stepper drivers. Quite a minimal setup.