Hi Leon and welcome to the slippery slope of astro-imaging.
I think you're right on the money when looking for a small refractor. You'll keep it for years to come. Get an ED80 or similar second hand. You can't go wrong. Check the classified here. An HEQ5 is a good mount for it. With a bit of TLC they work perfectly. How hands on are you? Are you part of a club yet? First, have a night out with the guys, talk to them, see the gear on display and when you're ready make your decision.