How to prepare for owner financing

[Sol Obarrio]

How should I get prepared to ask a seller to do owner financing? 

I am interested in a property that has been in the market for 3 months. The owner had to move out of town so I can not talk to him in person. I also know he has own the house for 9 years and he bought it at about 55% of the price he is asking now. 

I was wondering if I should prepare some kind of excel sheet with numbers, or talk to an account/lawyer first to help me out? As well should I do the process through the realtor or should I ask the realtor to give me his contact information? 

If you have any other tips please mention them as well. Thanks :)