RE: RV scenarios, which side to play ?
I can't speak for all SB scenarios, but they are usually scripted for both sides. When there is a recommendation on which side to play, it is often because that side is more challenging. The AI usually does an ok job as a defender, not so great as an attacker. So if there is not a recommendation, it is generally more challenging to play the attacking side.
It can be tough to make scenarios that are challenging against the AI and yet balanced for PBEM. Ozgur is the best scenario designer in the SB series and RV really shines as a PBEM game. You can only learn so much against the AI and so I heartily suggest that once you get the hang of the game, you drop a challenge here and see the real beauty of the game.