Here are some pointers about multi-engines planes(think I have had a total of 11) and what I have gleaned over the past moons of flying. For electrics, the direction of rotation turning towards the fuse or outward to the wing, really doesn't have that much difference in stability, but where I (and others in another group) found when the props turn outwards, the touch of the ailerons are crisper (not rolling the plane over, for turns) than if props are turning inward. I know some are laughing at this, but you should try it. Once you have flight time under the belt, you can even feel a stall coming on where you become one with the plane. The less expo, the more you can sense it.
For batteries, I use a 3300 mah with 2200kv motors and 10 x 3/8 props.. You will find that you can cruize around at 1/2 throttle easily and get flights over 10 min. Remember, the lighter the plane, the lower the stall speed. Also, where you position the battery makes a difference.
Now for thrust differential. Imagine this, you are in your 30 degree turn and the lower wing motor craps out. What is going to happen
a: if you have a moving rudders and you don't know what to do?
b: if you just have differential thrust and no moving rudder?
c: if you have both?
Now, what happens if you are straight and level and your right motor craps out if the plane is flying towards you?
Most pilots never address or think about that until it happens. So what is your emergency procedure(s) and what do you want to do for your build? My first multi lasted a total of about 4min before it was totally destroyed. Now, I have an emergency procedure for almost everything that is possible. Hey, foam is a lot cheaper for the learning process.