That's a loaded question on a forum site, but since it's new to you and has been sitting, I'd recommend just getting the Polaris kit with everything and using their standard fluids to change it all out and start with a known product. They should have a kit that has all the oils, oil filter, air filter, maybe other stuff like belt, spark plugs, etc. I'd start there so you have all the oils, and then add in the other stuff as needed to get a fresh start with all the consumables.Looking to do a oil and filter change. What's the recommended oil and filter to use? What gear oil is best to use as well?
I give this a try, I also want to pull the injectors off the engine while still attached to the fuel rail and see if they are pumping out fuel with the key on.I would personally take one spark plug out at a time and stick my finger in that cylinder to see if you are getting exhaust and intake. You should be able to feel if you have a major problem. If you have decent exhaust and intake it should at least attempt to fire. You will need another person to bump the key but it will be a quick way to get an idea. You can worry about an actual compression tester later.