Price seems pretty fair to me. You can always counter. Advice up to this point all good. Stuffing box packing will be dried out, so consider tightening the box hand tight plus a quarter turn. Once in the water running for a few hours, check again for any drips while spinning. It may need another adjustment once the packing material becomes soaked with water. A drip every few seconds okay, but none while at rest.
A nickname for the one cylinder Yanmars is "Thumper". You will see once you get it running. Good little engine. Best to get it running after changing the oil in both engine and transmission. Tranny oil should be the same as the engine. Bell housing should state what type. Does not take very much. Dip stick has a small full mark at the bottom. Do not screw dip stick in when checking; just rest the cap on the housing to obtain the correct level. Run it up to temperature out on the water in gear for awhile to get rid of any moisture accumulation.
Please keep us posted on your final decision and cruising experiences. Welcome to our cabal of worthy advisors.
We look forward to seeing pictures of your new boat. The boat's anchoring system is the most important safety feature. Be sure you have it set up properly before heading out, just in case Thumper decides it needs a rest. Our advisors have lots of information on all boating topics.
Also, before you bite the bullet, hire a marine surveyor to survey the boat. Even though the price is quite low, serious boating repairs can add up quickly. A survey will point out any anomalies that need addressing. Those can also be used to adjust the purchase price.