A V-tail has one big advantage: You wind up with a net of one less tail surface, so you save weight

The biggest disadvantage is the complexity of the combined elevator & rudder control, but this can be solved with computer radio mixing or pre-packaged V-tail mechanical linkages.

Answers to your questions:

A 90 deg. spread is about right, as the elevator and rudder effects will be equivalent.

A rudder always gives some a roll effect (funny, I just posted on another thread about this), both directly and indirectly, but a V-tail will produce a relatively higher roll moment, which is in the opposite direction of its yaw induced roll. The more obtuse the V-tail, the greater the direct roll moment for a given yaw force. This all means that a V-tail will, with pure rudder input, roll a little slower as it yaws.

Dihedral will always help lateral stability, but the net effect is reduced with short, stubby wings, as the lateral moment of inertia is less.

Also, short, stubby wings (such as on an F-16) have a small wing area, so they need higher speed to fly- consider this when designing your plane. Unless your plane is super light, even by park flyer standards, you may not be able to fly it slow, and you better have the motor to move it fast.

I can't answer your questions on motor/battery/prop setup for two reasons- 1) I'm not very familiar with typical motor sizes for given plane sizes/weights, and 2) you didn't give your plane's estimated size/weight!