Buy subto sell via wrap question

[Marcus Griffin]

Im closing on my 1st subto deal at $300K(240k mortgage balance, $60k Partial claim balance) Seller interest rate is 3.4% payment is $1900. I'm looking to wrap this to a end buyer for $350k at 9% interest 10% down. Should my wrap loan be for 30 years or should I include a balloon. Rent is $2200 in area. My 1st deal ever. Looking for experienced investor input.