Purchase a family owned financial planning practice?

I am in the financial services business, and have been doing this on my own full-time for 1 year, but have done internships and other work experience in this industry since 2002. My wife’s father has a very successful financial planning practice that he is wanting to slowly sell to me. He currently has about 800 families that he works with along with a large amount of 401(k) and health insurance that he manages. He wants to only work with his top 50 clients which would leave a lot of clients that I could service and work with. In other words an immediate client base plus I will get 20% of whatever business he produces to insure that I stick around. This would double my income next year and more than double it in coming years. I am good at what I do, but having an established clientele base would be huge for my career. My concerns are living close to family and having potential problems down the road with him and having a falling out. Any advice?

All reservations can be solved in a contractual agreement. That is what they are for.

Predict all possible problems in the future and write up a contract that will protect you both in case they happen.