Welcome, Dave!
I’m curious why you are removing the
furnace? We don’t use ours very often, but it’s saved a couple of trips where nighttime temperatures dropped into the 30’s. It’s pretty simple, and if it’s not working, there are just a few likely issues, not expensive (ours had a bad thermostat when we bought it). If you do remove it, you'll be left with the vent holes in the shell.
Either way- remove or repair- for safety I’d hire it done and have the LP system safety tested at the same time. For local recommendations, best bet is to talk to other RV owners in your area. Avoid big dealers and chains like Camping World.
Our 2008 lacked safety detectors from the factory. That’s something you’ll want to add if a previous owner hasn’t already.
The drain is also a very simple affair with a little hemispherical trap under the sink and a clear plastic tube to a fitting on the side of the trailer. Take it apart and clean or replace the trap and tube. Probably has some nasty build-up from previous use. Soak in soapy water with a bit of bleach and use a small bottle brush. If it’s really bad or starting to get brittle, just replace. The parts are cheap and easy to find. That one I’d tackle myself.
Congratulations and best wishes with your new trailer!