As I reread your post it throws up more questions than answers. The following is provided for clarification.
1. You appear to have decided on wide field imaging and are asking for mix and match equipment suggestions that will dovetail with your existing equipment inventory.
2. Your reference multiple imaging, are you suggesting you want to run more than one capture setup simultaneously.
3. You talk of working at f1.8-2.8, I consider this is a more specialist area that places higher demands on your focusing arrangements, backspacing and filter selection.
4. Most of your comments appear equipment centric as opposed to target specific. It would help if you specified the targets your are after photographing.
The range of equipment you list suggests you are already an accomplished imager, yet the context of your query seems a little confused.
I don’t understand how in your last entry you determined you start with a new camera when you already have a good range of cameras that are able to support your 300-400mm fl imaging aspiration. There are several good scopes available that will work with your current cameras at 200-400mm fl. A couple that would cover both ends would be the Redcat at 200mm and Esprit 80 at 400mm. However, there are plenty of similarly specified triplets to choose from.
Good luck with your search.