I am considering the possibility of selling 4 duplexes in 4-6 months and looking in to something larger.

If you’re currently living in a bad school district and want your kids in a better school district or some other safety / life choice, you may need to compete in this market.

My problem with larger MF is the initial cost.

Stick to fundamental buy-and-hold real estate...noting glamorous or fancy...If you have safe, clean, and appropriately priced units...focus on C-class value add, and maybe consider working with the local housing authority to accept housing choice vouchers, you will have long-term occupancy, debt paydown, and equity build for life.Investing is relative, and I doubt your main motivation to invest in RE is to contribute to the list of "25 fastest growing cities in the US"Best of luck

Spend a lot of time getting to know the neighborhoods in your market of choice. 

You don't have to seek an attorney's professional opinion, but they becomes an essential piece to your team moving forward the larger your portfolio gets.

Plus investors buy the duplexes that remain as duplexes and they often don't want to over pay.I would think that a large single family with an ADU would be worth more than either a single or duplex.BP fans seem to like the small multi-family because it can bring in a larger income than a single family and they think has less risk, less maintenance. 

We started a shared bank account and are on our way to setting up Wave as our book keeping software of choice.

I would suggest getting a recommendation for a cleaning person instead of a larger company. 

I think 3-4 days is the max I've had for vacancy that was the by choice so I could address a few things.