The rents are low right now but the landlord agreed to supplement them for 6 months.

Section 8 supplements enough on 3 of the units at a rate that off-sets initial mortgage payment.

I'm in Florida which is known for having higher property taxes given that we need to supplement not having any state income taxes.

But if you just want to start a company that can supplement your income and helps you invest I would recommend other options. 

I am not sure if it's the pandemic or something else, but it seems like all Assessors are behind, I have not gotten by new property tax yet, but know that I will have a supplemental tax bill next year because my Mortgage company has based my taxes off of old data.

Given your goal for cash flow to supplement self-employment income, I'm guessing acquiring more doors? 

The contractor or homeowner then has to arm wrestle and send in legitimate bids/supplement requests to increase the payout to fair market pricing. 

We just paid our supplemental tax bill so that wiled our savings away quick.

The goal is to supplement retirement income, have fun, and leave our kids something besides an unpaid Discover bill.

The biggest piece that blew me away was that they will supplement your rent if for some reason it comes in below the rent range they provide you with for as long as you hold the property.