Common concerns in pre-1940s buildings include outdated plumbing, old electrical systems, and structural issues that could be costly to bring up to modern standards.

Do you think the rising taxes might eventually become a bigger concern, or do you feel the benefits will continue to outweigh the costs? 

I’ve been looking into coastal options and was initially considering Florida, but the taxes have been concerns. 

My concern for you is that it appears that if the owner comes back, they only have to pay the bid amount + costs, not what you paid for the broker.

I am also concerned about possible mold in the basement.What should I do?

Basically the concern is they tie up the property, collect enough rents to make a little bit, and then just default.

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.

Amassing a lot of debt and being only able to make lateral moves if I sell is certainly a huge concern of mine. 

If you have one abuser, it won't affect everyone else systems.One thing not mentioned that could possible be a concern is were they are placed. ie. are they all positioned well for inspection and/or replacement if need be?

You have hit ALL of the areas of concern that I have with using my account for buy and hold or fix & flips.