Need Help With Contract

Yesterday i sold my rehab house for $35,000. We agreed that he would put $12,500 down and pay $375 over 5 years. Pretty much going at a 0% interest rate (Which i wouldnt do but the size of the down is good). My question is, how do i work up a contract? Do i need to get a lawyer? Should i buy my own insurance to cover the house to damage in case they cancel insurance? How do i pay taxes on this? I bought the house for $9,000 and put $5,500 in it. So after the down payment i will have about $2,000-$2,500 to cover the investment and then all profit after that. Should i start a corporation or LLC to do this? I have 1 rental house right now and plan on doing more. But if somebody could get me some info on how to work up this contract, it would be greatly appreciated.