Having an LLC is not necessary.However, it should be decided once you have a conversation with an Attorney and an Insurance agent.Some factors that come into play are1) Your Net worth2) Your Risk Tolerance3) Your Risk Exposure

Adequate insurance is generally recommended as a first line of defense and may play a part in this decision as well. 

I have no clue if she talked to any buyers besides myself at any point but without playing games I told her I could pay her what she asked for.

A lot of investors seem to be buying in here as long term defense plays.

Mailers are long term plays, expensive, and have a low success rate.

Defintely talk to a lender because there are a ton of factors that will play into the amount of next mortgage you can get- the biggest ones I dealt with were DTI ratio and the monthly payment I would have to make on that HELOC.

I got a notice in a condo that the music was loud all week and it was a noise violation. 

This "expertise" will fuel their next 9 misses, because they proved they were right in the past (this is where the ironic background music is piped in), until they once again show the world they know best.I guess if you can make it to the MLB Hall of Fame by being failing 7 out of 10 times, ...?

Unfortunately the building I bought in does not support STR but I still think its a solid play as a regular long term rental.

And it's completely up to you and the amount you are willing to spend.If you are planning on making real estate a long-term play then you should definitely be on the hunt for a good accountant and attorney.