Get to go slow and learn over time, build capital, and qualify for the primary res cap gain exclusion. 

I'm sure you will gain some interest from potential investors then maybe they can supply you with the down payments and you can pay them back over time and you could buy more per year.From what I know, business is a slow game and from what I hear, successful Real Estate Investing can be boring.

My Airbnb inquiries has been very slow, but again I’m just starting.

I dont agree with this thought process never have never will.. its all situational.. or as they say in RE location location location.in markets with slow to historic negligible appreciation sure it does not take a rocket scientist to run the math that if your negative cash flow and the house is not going up its not the greatest investment your value play there is tenant is paying off the majority of the property and your getting some tax bene's if its not bare land.If we used this thought process IE the only good deals are ones that are positive cash flow day one with max leverage  80% loans then as @Russell Brazil states no one would invest in the majority of the east cost and West coast and well Denver and other select cities.. everyone would be in the Rust belt and mid west or deep south in C class properties. wealth is created for most investors with appreciation full stop.. because most investors cant buy enough property or doors to make a difference when cash flow is 200.00 a month your not going to retire on that. your going to retire on paid for nicely appreciated property.

Then a pause, then they started up again briefly in 2019 as the economy was slowing and WHAM, COVID ZIRP policies.

I'm not sure that would improve your position by taking the tax/penalty hit (not sure of your age) you would incur by withdrawing money from retirement. 

Call me crazy but we wash every turn we use light weight quilts but soon we will move to Duvet covers when we refresh during slow season. 

My properties are in the North and it gets very slow during Winter.

I've been a little slow to respond and I apologize. 

Or slow Do people actually rent single family homes for $4000 ?