I don't have the experience that some on these forums, but I'm getting there. I'm in my 2nd year and have spent way more time & money than I meant to. I have built 4 MR's with 4 different flight controllers.. I have 9 cameras of which my hacked gh2 is my test camera, gh3 and gh4 are my main camera's for video, and gh4 and 5d mark ii for photo's, although I don't us the 5d much.
That being said, I bought 2 kits, and built the other frames myself out of parts. Using adobe illustrator, drill press and a band saw. I fly a x8 with rectangle arms (easier to keep engines aligned) for my main large rig and like it. Use kde 3520 (they work with more ESC's than the higher pole motors which results in a whole lot less stress and crashes).
I'm happy with my rigs but am constantly trying new things.
That being said, if I were starting over, this is what I'd do. Buy a f450 with gopro gimbal, (either the DYS 3 axis gopro or DJI's if the extra money wasn't an issue) with the V2 Naza & GPS. That would be my fly the crap out of it have fun and get lots of flying time in. Alternative would be DYS gimbal with Pixhawk if I wanted more features.
Then I'd probably buy the DJI 900 with either a Naza V2 or Wookong. I'd fly that with a gh4 and if wanted better photo's, I'd sell the 5d and buy a 6d (photos are the same, video isn't). 6d weighs 26.7 or 755 grams (body only) and 5d mark ii is 956g/ 33.7 grams. GH4 is 560g/ 19.75oz. I'd check with peeps on the DJI 900 and see what they think on the weight difference. I'm guessing your ok. I'd buy a $800 or so camera gimbal with Alexmos 32 bit board and use that for a bit and then if the Phobotic controller works out, put that on it.
Alternatively, I'd build another x8 or hex with square arms or buy a frame kit with square arms. There are plenty out there. I went with Avroto's 3515 and KDE 3520's which I'd stick with as there aren't ESC / SYNC issues that are all over the internet with guys falling out of the sky wrecking expensive cameras and rigs. I'm not sure I'm right on this, but when I check flight times and voltage on Ecalc, there doesn't seem to be much difference.
If money weren't an big issue, to save time, I buy one of the sturdier frame kits and build it out myself. Again, I'm fond of square or rectangle arms. Which means only a handful of frame types.
One issue you need to figure out before building/buying a kit (which isn't an issue on the DJI 900 as it already has retracts) is if you want 360 degree on you gimbal. Then it's' either retracts or a revolving landing gear. This takes some thought as it adds to the weight and you need to figure out lifting capacity with your all up weight. AUW... DJI 900 is easy, cause it's ready to go. Just add a gimbal.
I'd be looking at Hexcrafter (on the high end of frames), Sort of high end, but less expensive would be VulcanUAV (aluminium rectangular arms, easy to customize) or Carbon Core (fiber carbon rectangular arms). If I were to go with round 25mm carbon fiber frame, I'd look at Quad Frame USA (if your are in the USA). If I were to add another MR to my fleet right now, I'd either custom build another with square arms and cutting my own plates and motor mounts or buy a quad frame.
There are lots of people using the Tarot frames, so I certainly would consider that. Just would take a lot of googling and asking questions.
Motors, flight controller, and ESC's are also going to take up a lot of your time on research..
In my case, I fly more minutes on the smaller quad with go pro. I sometimes I marvel at the footage when the go pro isn't tested on exposure. I've seen some pretty good footage out of that and sometimes I wonder why I spend so much time and money on the bigger units. I like the better quality and the stability of the bigger units in the wind, but it is more stressful to fly. If you go with a DJI naza on a small unit, I'd probably go with the DJI gimbal as I've seen some nice footage.
Have fun. Lots of decisions.
