On the one hand you could buy a turn key duplex or tri plex in Cleveland that cash flows decently, or on the other side of the spectrum you could MOVE to Cleveland, house hack a distressed 4 plex using FHA with 3.5% down (~7k), rehab this (~20k), then refinance out in a year using a local credit union to recover all of your money, all while BRRRR'ing another single fam house, then repeating the following year, to accumulate 15-20 units in a few short years, with the plan being to expand into mid sized multi fam vs syndication after that.

I try to keep the comps within 10% but if there's a difference of a hundred sq. feet or so I'm not sure what degree of adjustment to make although I'm sure it depends on the size. 

Nah, I'll pass, if I am really desperate I can offer the project for 13% less than what I am willing to pay, but this size chunk makes it unattractive to investors and good contractors.

@Joshua McMillion mentioned one way-ROI.When it comes to real estate, returns come in different shapes and sizes.

How are the lot sizes? 

Are there other methods like a fixed dollar amount based on the size of the house, age of the house, etc that you use instead of a percentage of rent?

Now, in 2021, rent is minimum $1,500 on up, depending on size and proximity to the beach.   

I haven't found any tool that can find 'all' as much of the time the reporting of data by the county/ municipality can differ and many times the tools are built one size fits all.Good luck!

4) What size properties work best as rentals?

There are lots of ways to withdrawal funds from retirement accounts prior to retirement (Roth contributions any time, 72t distributions, Roth conversion ladder during early retirement, or simply pay the 10% penalty).Any advice beyond this point would require knowledge on the size and composition of your your traditional 401k and your personal tax situation.