New to this in desperate need of advice

[Ms. T]

I am in the process of tackling my first deal!!

I have two properties that I am thinking about buying for 45K/ ea.  They currently are both rented to Section 8 Tenants  for $750/mth.  With a few moderate upgrades I can bring the property value up to 65K within 2months.  

The seller wants me to put down 30% (27,000) and he will carry back the mortgage for 63,000.  I need to know what you think is the least amount of time that I should accept for repay. 10? 15? years?  Is this enough leverage for me starting out?