That's overkill just for one platform (or do you mean for the whole craft?).
For just a platform you might find using an Arduino plus a small 6DoF or 9DoF sensor board easier to fit - the accelerometers should be fairly central on the platform ideally (although its less crucial on a stabilised platform than on a true IMU).
So you need IMU software to measure and calculate the state vector, then provide feedback loops (perhaps with PID) to the axis motors/servos. Manual input would program a "desired state" and the differences are then used in the feedback.
There are two basic approaches, one is to measure craft orientation (which you'll be doing anyway) and calibrate the servos to correct for current orientation (open-loop).
Secondly the closed-loop method where the platform measures its own orientation and uses feedback to correct - this I presume is what you want "standalone stabilized gimbal".
The PIDs are what you'll tune for smoothest motion, compass (9DoF) needed I think (unless you can tolerate slow drift in compasss heading).
eBay has some 6DoF and 9DoF boards, mainly I2C, and some are 3V3, some 5V, some do both I think.