Was it easier to dig the foundation with shovel, horse and scraper or with a track hoe?

Given your experience with RV parks and MHPs, you already have a strong foundation for managing mixed-income streams, which will be valuable here. 

You can save and have a foundation to do your first fix and flip

Multifamily is all about relationships, and it sounds like you’re building the right foundation.

-Creates a solid foundation for passive income, allowing you to reinvest future cash flow into other opportunities without as much financial risk.Cons:-Ties up a large amount of capital that could potentially be used to generate higher returns elsewhere (like another STR or other investments).

Quote from @Elliot Rosen: Use a licensed and bonded foundation company and keep the invoices, and disclose it to the buyer.

It gives you complete control over the property and helps you build the foundation for future growth.If you're planning to expand your portfolio, I strongly recommend partnering with a professional management company.

This is just the foundation.  

They will do a slap dash job on a house that still has a bad roof and foundation in a neighborhood that will see zero appreciation. 

Your top-notch experiences and resume will provide you with a strong foundation in real estate investing.