I think its worth considering how tempted you'll be to upgrade and change your OTA too, even though you obviously need to take into account what you have right now.
I'd humbly suggest a list of "dream objects" you'd like to image might help. Some people lust for galaxies, others widefield nebs. You do go through phases. Earlier on, we all want to be able to image everything of course
FWIW, I found my QHY9 mono worked really well with MPCC on a stock F5 8inch Skywatch newt. There was signficant vignetting that could usually be processed out but made mosaicing tough. I eventually lusted for a wider better corrected FOV and went FSQ and now the smaller pixels are really paying off. Its true you spend a lot of time fiddling with adaptors, stepping rings etc, but if money is an issue then QHY lets you at least get entry to CCD imaging and you can add more goodies as the budget allows. At your focal length, you probably realise good guiding through a piggy-backed scope is not a given, and OAG setups for Newts have their challenges as Peter describes.