If you plan multi minute (I think you should plan for multi-hour) exposures then you will need *very* stable tracking on both axes. Do you have anyone who can make Direct Drive motors? I have seen it done for "amateur" telescopes but it takes serious skill. What about bearings, again for both axes. Forget about the usual dob bearings, they're ok for mere visual, but imaging is a whole different level.
What about field rotation? Big field de-rotators are expensive, and you will want a big aperture to pass the light cone. How about cameras? For something at this level I'd be looking at a 16803 camera, or even a FLI Kepler 4040. Not cheap. Plus, of course you're putting all this stuff on the end of the truss tubes (Another reason why big 'scopes in the 800mm and up class go for Nasmyth systems.
Guiding? I assume an OAG since encoder guiding will be even more expensive and you could end up with something like This.