That seems to vary widely from state to state.

Rehab costs that are under estimated by very wide margins.  

My husband and I started our property management business about 18 months ago and absolutely love the service and peace of mind we are able to provide to clients.Percentage of income is often how people charge but this varies widely by location and also type of rental.

In Florida, land trusts offer some unique benefits similar to an LLC, such as asset protection and anonymity, which makes them especially appealing in creative real estate deals.While LLCs are often more widely used because they’re familiar to investors and offer clear liability protection across multiple states, land trusts can be highly advantageous in Florida due to the specific protections our state law provides.

We ensured every home had a wide collection of quality cookware, spices, coffee, etc.

They need a wide berth.But, the good part is that we have a blank slate to work with.

A mold remediation business will be able to tell you the extent.  

Google search gives me these super wide ranges and mostly talking about adding a bedroom in a SFH, which I'm not sure if applicable to this situation of "moving/subtracting a bedroom from one unit and add it to another unit in a duplex". 

At the same time, I would reach out to that STR owner to try to get him to fix the nuisance issue.That said, even if you are successful in staving off the issue for now, it could come back at any time based on the current board members or on wide community support for getting rid of STRs.You could try to gather support for changing the covenants in your favor, but my gut is that that will be hard to do. 

In addition there are areas in Los Angeles that have stricter rent control than the state wide rent control.