~About 10% of first year of annual lease. 

At a 5% interest rate on a thirty year mortgage, that’s $1,176 that the tenant pays down for you annually.

@Nathan G. good point😊If I would like to keep 100% occupancy but also take care about my income and amend the tenants contract with annual rental increase +3% just to protect cash against inflation, HOW they can react to that❓

For example, if your net cash flow is $3000 per year, and your annual depreciation is also $3000, then your net taxable rental income is $0. 

You could review their usage annually to determine the monthly bill amount going forward.

The rental property owned by the LLC is a good performer...market value of about $300K and generates NOI of $20K annually.  

Sometimes accurate vacancy numbers are hard to get unless you ask for a detailed T-12 or annual RR, and then figure out the vacancy rate yourself.

A new fridge is approaching 8% of one unit's annual gross.  

Or you could simply write in that annual rent increase will apply and to be determined.

If you live in a state that's cheap to form a LLC and cheap to maintain it each year (annual registration fees etc), then it may be worth it assuming you can get around the lender issue.If you can, diversify like what the others said.