I liked the original Combat Mission WEGO system for PBEM quite a bit, which I think was like this:
First player enters orders, second player enters orders, first player calculates outcome on his rig, records playback, enters orders for next turn, second player enters orders, jump to 3
Due to the tactical nature, each turn was 60 seconds and playback was in real time by default. Since then the CM engine was tuned for real time, not sure if the original PBEM sequence is still possible with it.
Not entirely sure if this method can be applied directly to your approach. What I liked about it is that one could replay the last turn several times from different viewpoints and get a better understanding of what's going on before entering the next set of orders.
As finding players for a scenario is at times a bit tough via forums or chat or email, the slitherine guys have setup a very good system for their multiplayer games: Any player can setup a 'challenge' which will be published through an in game browser. Any player can accept the challenge and a multiplayer game starts were the turns are exchanged via a server by slitherine (I guess). For settting up private matches, a password can be tied to the challenge, so only the player knowing the password can accept that challenge.