Don't shoot yourself in the foot by supplementing the tenants' rent and shorting yourself or your family. 

(We're currently putting 100% of my income toward our mortgage and would add the supplemental income, as well).

Landlords must now provide an opportunity for the applicant to submit supplemental evidence to explain, justify or negate the relevance of potentially negative information that may result in a criminal denial.

You may to supplement that with an accounting software such as Stessa.

1st Lien Heloc of 300KGoals: To acquire as much rental cash flow/assets as possible in the next 5 years prior to retirement for supplemental income, and purchase a new primary residence.Deal #1:  My mother owns an investment property that is currently tenant occupied thru June 2022 @2K/mo. 

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.