Either way, I would be looking to have the rent at least cover the mortgage payments, allowing me to save up for my next buy and hold (of course after paying for taxes/insurance/ repairs etc.)

ATLANT calls itself the "Worlds Real Estate Blockchain Platform" and the whitepaper discusses, in depth, the idea of tokenized real estate ownership and the use of blockchain technology to create more efficiency and ultimately lower costs of real estate transactions. 

You should also have been and continually shopping local smaller banks and CU's working with their commercial lender on something that works, if you have some cash saved, a decent job/income, and a good credit score, you should be able to get fix and flip loans fairly easily from a small bank.

Its a young husband and wife couple that is just starting off their journey living with each other and saving for a home.

Ideally I'm looking to house-hack a 4-plex and get ~1000/mo cash flow from the other 3 units and just save until I can start snowballing properties.

What ultimately helped you decide to take the plunge and purchase an REI property?

These are things that will ultimately determine the maximum size you can build.Also, $0 for architectural fees is unrealistic.

I feel like getting more units should be the fastest way to expand, but am I better off buying a bunch of SFHs and working my way into apartments or should I save and wait?

set up a meeting and make a proposal ,simplicity and straightforwardness is best and saves time  Good luck 

A lot of companies will send you pre-sorted first class, but if your pure motive is saving money, don't use that route.