First time- Seller Financing for 4plex

[Janice V.]

This is my first time as well posting, my apology in advance if theres possible confusion.

Anyways.. let me give you some insights. After months of speaking to seller he finally agreed to sell his fourplex as he has been self managing this multi family property. Him and his wife are in their 70's and  I asked to let me take over the property, pay some cash upfront and if he can carry the note. He wasn't planning on selling. Theres no rehab been made since he acquire it back in 2002 and haven't raise the rent. 

Heres the breakdown;

4 units

2bed/2bath

Rent $600 (under market) $750 is whats going for next door

Selling for $125k (next door fourplex sold last month $280K)

will give him $25k cash and $100k seller finance.. Now this is where i don't know what to do next? Ive read a tons of books how seller finance work and to structure it BUT what i don't know whats next after that.. after agreeing with term etc. then what?  Do  I go find real estate attorney and draw the contract or find mortgage originator and servicing company? Ive worked really hard to find this deal and don't want it to fail for not knowing what to do next.

I gladly appreciate any help and suggestions. Thank you!

Janice