With an intense market and the appetite for investors, many 4 plex sellers are not accepting FHA loans.

If not you're going to need one anyways and they can go over lot of this.1031 rules in general can be interpreted differently depending on your risk appetite, but a lot comes down to intent.If you need a intro, I can help and share my experience of how I handled a similar situation...

I also learned there's very little appetite for refinancing properties under $100K.

However, I don't know what the market's appetite is like for primary homes with solar.

There is a really strong appetite for both property types and I don’t feel one is easier than the other.

Also, with the small lenders their appetite may or may not include doing these mortgages.  

It's almost as if my ad is being suppressed and I'm saying this because for $9.99 a week I'm getting 12x....yes, 1200% more traffic for the same units on Zillow. 

All of the work to suppress noise will be done through the basement by removing sheetrock and then doing whatever is necessary to eliminate noise.

You can find out which banks have an appetite for mobile home parks by asking the MH/RV brokers in your area, networking through other owners of parks in your area, or simply obtain list of the smaller banks in your area/region and call them to see if they have lent on parks in the past.

If the bank does 70% and the seller carries 25%, then you would only need to come in with 5% down and closing costs.All depends on the banks in the area and their appetite for these loans at the moment, but could be an option.Good luck!