1) Yes, you need to change your oil/filters now. Lightly used engines can be more demanding on motor oil as moisture builds up and contaminates the oil. The same holds true for the fuel system.
2) 10W-30W should be fine (or even preferable) as, by definition, it will give you the cold start lubrication advantage of a lighter weight 10W oil, with the higher heat/load protection of a 30W oil. But, I would run it by John Deere https://secured.deere.com/en_INT/htt...tact_form.html just to be sure.