What a rare find with only 36K miles. Volvo parts are easy to get and reasonable priced except from the dealer. My local Autozone stocks an amazing amount of stuff for my 87 240 wagon. Places like IPD are great as well.

I would recommend finding an established independent Volvo repair shop that knows 240's and let them look at it. Coolant, engine oil and transmission fluid changes are a good idea. P/S, brake and rear end fluids are a good idea but to me would be a secondary priority

I would replace the timing belt. Inexpensive and will keep you from getting stranded. Yours is most likely the original and in need of replacement.

Good luck with it, that is a priceless find. I am on my 6th 240 and have loved every one of them. They do have their quirks but overall are great cars