Is there some form of paperwork my partners should have to properly claim this expense?  

Is there any benefit to installing a home security system for each unit?

I am looking to inject (contribute) some money into one of my LLC to finance some new acquisition this year.I am refinancing my home (that is under my own name) and will use the cash out as contribution into the LLC.It is my understanding that while you can't deduct new mortgage or refi anymore on your personal home, you can still deduct all its costs when it is used for investment (by deducting from the investment income/gain).What would be the proper way to document this transaction in addition to the schedule recording the contribution in the LLC book?

If you don't do this properly, and you have an uncooperative tenant, you could dig yourself a hole quickly,It's been my experience that cash for keys is very effective.

My goal for Q1 2019 is to create the proper organizational structures to put these assets such that we are not exposing each other to unnecessary risk from a liability and tax standpoint.

After I take possession of the property, I want,to install a new LOCKING MAILBOX for my unit. 

If you are flipping/selling the property to an end-use, you may want to think about using premium flooring throughout, which would mean installing all hardwood.

What would you consider a fair price to setup an LLC properly? 

Also, how much does your recommended option normally cost with installation?  

We had a security system installed into the home due to unsavory individuals looking to find some tools at a discount.