So in view of the weight of the lens alone of 427 grams, together with the body we are already in a kind of limit area for the gimbal. The M3 is very strong, you can set the engine power to maximum, but don't expect miracles. I mean the M3 website also has a list of compatible lenses so you can get an idea of ​​what the designers are giving the go-ahead for. I keep reading that people with lenses > 400 grams have been able to successfully stabilize the camera. But you shouldn't expect miracles from the different gimbal modes 

Balancing works perfectly, only the additional functions (record button, exposure wheel) work without an additional Bluetooth module, which is only available from Sony at the moment. 

Should definitely be balanced in terms of weight if the lenses are not too big. A Sony A7III is also possible. However, the additional buttons (recording, exposure) currently only work with Sony. But all other gimbal functions work. 

I don't think much more stabilization is needed, but of course you can activate both.