Hi guys, I want to get started towards building an S900 setup to fly a Pocket Cinema Camera or a GH4.... I'm not in a position to build that full setup  just yet, so would like to build a lower-spec, intermediate setup first.

I had it in mind to go for an S900, an A2 controller and to try and use a GoPro, Zenmuse gimabl and FPV transmitter for my iniitial setup- planning to upgrade as I go.

I do know that an S900 is *massive* overkill for such a small camera + gimbal setup, yet going for just a Phantom + zenmuse will waste some money & familiarisation time on the Phantom.

Is this a possibility?

why not, it's an nice copter, but i would buy it with an GH4 Gimbal and H3-3D for your Gopro

OK, but I'd like to know if a H3-3D will play nicely with the  A2 control system??

According to the DJI release note dated 1/19/2015. The H4-3D will work with the A2 systems and the Naza systems.  The H3-3D will need to be updated to work with the A2 firmware V2.5  Hope that helps

Great, thanks very much for the help! Currently working out some of the broad details of the build

Let us know how you do.