Redcat 51 is quite good:
https://pbase.com/gregbradley/image/169325610/large
Galaxies using a small refractor is a bit unrealistic unless you intend to image the Large and Small Magellanic cloud. Perhaps Sculptor would show up well enough.
Nebulae though is realistic.
The Zenithstar 73 sounds good if it meets your budget.
It would be near the limit for the Star Adventurer.But you can capture a lot by using 30 second exposures and lots of them and stack them.
Greg.