If so, then I would return the portion of the security deposit to the one leaving and collect that same amount from the one staying. 

Even with multiple units, with current interest rates and a competitive market (prices have continued to rise even with higher interest rates) think the Madison market is a stronger long term ownership strategy, where the bulk of your return will come when you sell from appreciation in rents and property value. 

Also, running a flip with no money and hoping you get a good return with all the other stuff going on in the background starts to add stress, and you end up not enjoying it.

You'll end up with a dog that you can't unload at the end of the day when you've dumped thousands of dollars into it with no positive return. 

So far, it's been an effective strategy, and I've gotten some really good returns utilizing it.I think more property managers should consider it.

Now, with me being back I'm returning to my original plan of wanting to house hack in the Greater Boston Area.

I've had low returns but in general all have made money.

What’s the best way to determine if a lender specializes in conventional, commercial, hard money, non-QM, or DSCR loans?

This sounds like a solid return!

But since it was being used for investment when you sold it you also qualify for a 1031 exchange.If you find that you still have any taxable gain leftover after the primary exemption, then you can indefinitely defer that tax and not have to recapture any depreciation in a 1031 exchange.