You could be drop shipping from an Amazon warehouse business using leveraged inventory and doing the exact same thing or borrowing billions to buy NVIDIA GPU's to retrofit and add on to your own servers like my favorite business does, SMCI. 

Is Water backup endorsement important to add on?

I heard that mentioned in the recent episode of the Rookie show too, and would love to know more about what platforms exist out there for the direct booking/purchase of add-ons in the STR space.

For example, in some cities you don’t need to add a parking space for an ADU where you would need to add one for an additional unit.

I will add one important fact here since you have a preference for Roth funds: In case you have a Roth IRA already, you are not able to transfer this to the Solo 401k.

I just want to add one additional thing to think about.

Just to add on to what @John Warren and @Sarita Scherpereel said security deposit rules in Chicago are very very strict.

That is pretty standard in my market and if I am not mistaken it is more like $25 dollar add on here roughly.    

Add one if you need it, but otherwise, if you are looking for ROI, there are better ways to do it.

You have to know what a Lot in that area is selling for and add on the cost of NEW Construction in that square footage to really know anything.