There are some great tips here and I have one other one: Never climb in a turn after losing an engine. Always make a slight descent in turns and it will not bleed off speed and will actually help with stability. If you are very low then you may just be screwed. Unless you are over a *****ly pear forest just chop the throttles and put it down. Better to make minor repairs than to trash a plane.
One more idea is to use three or four engines. I built a quad in the 1990s and am building another now. It is tapered and swept 25 degrees with span of 82 inches and four OS .46s. Losing one engine is not a problem although losing two could be an issue. I agree completely with Ed about tuning engines. I have seen more than one twin lost after the owner tuned them together which effectively leaned out one engine. Just tune to taste each, refuel and take off.
Another idea for a good twin is to take an existing foam wing kit and build a center section that can be joined to a left and right wing panel. By doing this you can put two fuselages on one wing which will double the vertical stabilizer area. Each can have its own radio if you can link two receivers to one transmitter (Futaba). I used two Sig Kougars and, later, when they were flown separately and one crashed I just bought a used Kougar and kept flying. This should work for many sport models.
There are many various multi ideas out there including tri motors which I have had. Since this is supposed to be fun just get what makes you happy and go fly!!