I have just gone down the same path having purchased a VQ Models P-61 Black Widow ARF.
The next step was to read all I could find on twin engined planes, how best to set them up and how best to tune them.
What I have done is to add elements for reliability first, on board glow, fuel pumps. There are others such as Twin Sync but I had to draw the line somewhere.
Next I added a Gyro to the rudder. I already had one on the ailerons but after reading some articles on work some one did with twins and they even managed to take off and fly successfully on one engine, because they had fitted a gyro to the rudder. It will also catch the dreaded engine out spin at least until you have a chance to realise one engine is out and make suitable preparation s to land.
The Widow has had it's first disassembled inspection by our heavy model inspector and is now ready for ground trials.
First flight should be in a couple of weeks.