DID, RK and EK brand chains are all quality. JT sprockets are nothing fancy, just decent, durable steel sprockets, and I recommend them. Excellent combination of cost and quality.
Far as sprocket sizing, just stay with stock.
1990 EX500 - 119,000 miles as of June 12th, 2017
1993 Ducati 900SS - Minty fresh garage queen
1988 Honda XR600 - Street legal play toy
*I have a large inventory of used factory EX parts, both gen1 and gen2, feel free to PM me if you are looking for something*