Mainly buying up LTR'S for cash at a deep discount. 

I have a rental property that has a main house and an ADU on it. 

Main thing for you is: - Have both you and your buddy talk to the same lender and get pre-approved to understand down payment options and what your combined budget would be- Decide how you want title held (joint tenancy or tenants in common) - do a google search on this to see which option is best for you guys- START SHOPPING!

Financing the deal with private money was effective for quick acquisition and rehab, which added substantial value by making the property more desirable for tenants.The main lesson from this investment was the importance of careful property valuation.

One of the main reasons is that almost no one will actually have a property manager on a duplex.

What a great analogy lol Not decided on that strategy, just researching about that specific one.The main reason was because a land trust can be a co signee on a conventional loan and can help with transferring the conventional loan to an LLC later one without triggering the due on sale clause

Year to date, we’ve seen the strongest home price growth in three main areas.

If your main concern is on the refi end the you could also move some properties into portfolios (just make sure that you truly plan to keep these as they may have partial release fees attached).

I also won't mind collaborating with someone for the main time.

That will impact any future offer prices.I bought a townhome with a broken lateral that was a short distance to the main.