We have a basement that was used as a dwelling unit, but not permitted by the previous owner.

You will need to find out if your umbrella policy will be allowed to go overtop of your rental dwelling. 

Our specialty is 2-4 units dwellings :)I might throw in another $50-$150 if I know something big is breaking soon.

They may provide instant income upon purchase, but that could be thrown away by having to evict them or pay for damages that are not covered by a security deposit that you did not set!

And what if the dwelling wasn't rented out yet, does that pose a financing challenge as well? 

My thing was wholesaling might be simpler with less capital and it would give instant cash opposed to a property that requires time and lower monthly cash flow.

Why not use the banks money to get your home/rental to your liking...And some instant equity...Am I right?!

Arlington county has relaxed its standards for accessory dwelling units (https://housing.arlingtonva.us/plans-reports/accessory-dwelling-ordinance-update/).

Why not use the banks money to get your home/rental to your liking...And some instant equity...Am I right?!

Rent Roll with specific dwelling number, name of resident, move-in date, monthly rent, amount of deposit held, current balance, additional charges, number of occupants, and a brief history of the resident (good resident / bad resident, special circumstances, etc.)