Take a camcorder. If not, take a pen and paper and prepare to write A LOT.
Key points to pay special attention would be the location of fuse/breaker panel, the location of the bypass valves (if you winterize) and the valves outside for your tanks and the low point drains.
Make sure they turn on the furnace for you during the walk through. It will smell for a few minutes, but better to do it at the dealer and make sure it works.
Also have them show you how to retract the slide manually in the event you have to do it manually.
GOOD LUCK and CONGRATS on your new purchase!!!!!