Most any 10W-40 or 15W-40 oil is good. 20W-50 is good for hotter weather. I believe 10W-30 is too light.
I would use Shell Rotella (or Castrol GTX).
Motorcycle specific oil is OK (I don’t use it.)
I would change the oil every 1,000 to 1,200 miles (The air-cooled Rebel 250 has no oil filter)