Vrbo has free price automation and analytical tools to compare the competition and see trends.

If there issues that need to be worked out with the 6-unit property, I would utilize that as a negotiating tool to work out a seller financing strategy with the current owner. 

I've tried many other personal finance tools and consistently had problems staying connected, so they're the exception.

I use a combination of their messaging tool and direct messages/calling.

@Shuvrajit Mukherjee agents already have tools that do a lot of that like Remine or Realist.

Be sure to check out the free tools BP provides to help analyze deals you may have and also market insights.

My concern is whether the city could deny permits for these modifications, such as removing walls or converting a garage, or if they are mainly just concerned with safety and habitability.

Not a right or wrong answer based on your investment horizon but a good tool to use.

BRRRRs are a useful tool for the right scenario, but it sounds like you have the opportunity to buy a house with basically no cash in, and with probably some of the cheapest financing available.

This is an essential tool for anyone buying a tenant-occupied property.