I really wouldn't worry. VASSAL is great for many things - bringing people together from all around the world, particularly for a little-played game like Epic; allowing you to test extreme armies without needing to buy models or proxy; etc - but it isn't going to replace tabletop gaming! You can zoom in and all, but it's still fiddly and time-consuming.

One other thing with CAS is it's similarity to Thawk Destructor in Lord Inquisitors xenoshunter list. However my opinion is that the Destructor isn't really needed.

Well, my version probably won't have hellstrikes, so they need not be identical. You can still have yours vary slightly, although it would be neat to get them to match up exactly. So we would both use the same "chassis" - Thunderhawk+turbolaser+twinlascannon - and you replace the transport capacity with bombs or missiles.

I've said this before, but I don't see why you're so worried about giving them transport capacity anyway. After all, there are no formations in your list that can actually start the game inside as they have to have transports (apart from bikes perhaps?). Thus the only time it can really transport marines even if you do give it the transport capacity would be as an air-evac after they lose their own transports.