The one item I see on your list is that you are planning on park owned homes, on paper that looks like a good idea, but I think that gets away from the advantage of owning a MHP. 

They also do not work in a timely fashion so if it’s a rental that could be a problemJust food for thoughtFor us what we make sure we do is service and maintain our equipment like hvac and appliances which often leads to longer life spans

When you do all items, the numbers add up to a large monthly expense   So what did my spreadsheets show me?  

Builders typically charge 2-3X the market rate for those items, which becomes a new profit center for them, since you'd be throwing that credit away if you didn't use them. 

-Unless the garage already has electric and water connections, that's an important and expensive item in the SOW.

But if you want access to the benefits that people like me have contributed to, and collectively spent decades and god knows how many millions of dollars building, why would you think you should get access to those items for free? 

He added a construction hold back and other items.

@KarlB- That's also another way of looking at it...good food for thought.

I recently switched insurance carriers for two of my rental properties and about two months after coverage started, I received a letter for each property with a list of items to be remediated within 40 days or coverage would be revoked.

Due to item 1, adding an ADU can require years to start achieving any return (once the accumulated cash flow recovers the initial negative position).4) Adding an ADU is a slow process.