To answer a couple of your questions directly..... our unit is a GE micro/convection of standard residential size. It is either/or, will not do combined energy sources.
Q2... the turntable is usually used in micro mode. Could use it in convection I suppose, but there’s no point. The advantage of convection is the air circulation, so you want the item on a rack, so the air can flow all around. If you’re doing something in microwave in a square dish of some sort, then yes, the diagonal measure of your dish would have to be small enough so the corners don’t hit the walls of the oven as the table turns.
Q3.... yes, you need the air to circulate in the oven in convec mode, but a fairly small space will still work. I bake cookies fairly often, using some half-sheet pans I’ve had for years. They fit on the oven rack with about 3/4” space around each side. The cookies come out just fine.
I find my oven does very well using the same time/temp as called for in a regular oven. That said, my m/c oven is original to the coach, so it is 18 years old and I wouldn’t vouch for its calibration!
John & Diane, Fulltimers. RVM103 NHSO
On the road since June '12 with Lincoln, the guard cat.
2002 Dutch Star 40, Freightliner, Cat 3126, 2004 Element