GH5 + Nauticam. WB really does work, and 4K 50/60 is just great to have. 10-bit 1080 50p, 10-bit 4K 25p, 1080 up to 180 fps, 4K up to 1.... someone on here said they could not really think of what more to ask for, and I agree. In practice DoF depends on aperture surely? I use the PZ 14-42 3.5-5.6, and DoF isn't really an issue. I guess with your +5 diopter you would have to be careful, but one of the great advantages of 4K is that you can crop and still end up with a full HD image, so you don't always need to be fully zoomed in underwater. Also, 50p slowed down to 25p in post looks very smooth. I don't do macro, but the best macro stuff you see on vimeo etc seems to have been filmed with a tripod. Don't forget that you'll need a decent computer and good NLE to edit!
Just my 2 cents!