The property is located in North Miami, FL.

First, take your client requirements for size, type, cost, location, etc. and develop a list of properties that fit. 

The owner wants to minimize the capital gains tax he pays so we want to suggest to him to do a master lease to us for "x" amount of time, and we pay his lease fee and hold the rest of the money in this time we will secure a loan to buy using the money we make as part of the down payment.

You forgot to put your location in your profile and your post so the answer is unknowable.

This takes forethought and planning that you can search the forums about.I think you will find your potential seller financing path challenging - not for what it is, but for trying to find those properties that will fit your timing, as well your scenario - whether it being the right size, condition, location, the right terms, etc. 

Simply use the search tool located at the top right corner of the site.

While the cash flow looks attractive, I am concerned about the long-term viability of the investment since the location is not ideal and these are older, albeit partially remodeled, mobile homes. 

I live in California but my primary investment location currently is Cleveland, although I’m looking at other locations as well. 

I am considering branching outside of Utah for some apartment complex purchases and this is a major factor in my location criteria.

I would not do this location unless you plan to scale in the industry.