Your biggest challange right now will be to get a good project house under contract.

One of the biggest things my wife and I are working on is building our team.

Here is a better description: https://joefairless.com/top-lessons-from-every-best-ever-conference-2020-day-1-session/This was one of my biggest takeaways from the conference.

My biggest question is whether I have the legal ability to build a 2 car garage that can hold a campervan's height with an ADU above it, or do I need to consider 'popping the top' in some realm and keeping putting the ADU above my property. 

Overall, I think house hacking is one of the lowest risk ways to get into investing, but the downside of it going badly affects you personally.

The two biggest benefits of turnkeys in my mind are: 1. someone else is doing all the work for you.

The biggest thing is to check your local area for their "means of egress" standard.

In your case the biggest thing I see is that with just a few partners, liquidity will be your biggest hurdle.

That's usually the biggest obstacle to refi, IMHO, because you usually pay that upfront.

Once you have long term financing in place are there any downsides in spitting the unit into 2 for cash flow?