I am the only real estate investor with my bookkeeper and at first she thought this was a little overboard but once she started setting rules in Quickbooks to simplify her work she quickly realized how simple this method makes things.

Can I still do simple 4 box calculation? 

I don’t have an STR myself but have helped a friend set up and manage a couple last year and it’s not as simple as it used to be. 

It is really targeted at gross overuse. for sure. i just ensure it's in the contract to that I can exercise the RIGHT to charge it if I want to. 

Your mentor has needs; try to meet them and develop a mutually beneficial relationship.A mentor can benefit your growth, but it's not as simple as one post on a forum full of strangers.

You can secure the property with a promissory note drafted by a lawyer or a title company, but keep in mind that “taking back the property with the note” as it is often pitched by gurus is not always actually that simple.

It could be something as simple as a toilet running. 

Exercise caution and explore alternatives before considering them

Do plenty of research and find out what other mistakes have been made in your are and learn from them.Both are great options but maybe doing a simple pros/cons list for both STR and LTR.

It is a simple value add.Get the permit and enjoy an easy value add (assuming it is close to $8k).good luck