Only the interest can be written off (and other operating expenses and depreciation) - paid down principal cannot. 

I currently have three properties that are 30 years loan with about 5.3 interest rate should I go ahead and start refinancing them into a 15 or 10-year loan or Do I just keep the original loan and just pay more towards principal to avoid refinancing and still keep the same cash flow.

If you were cashflow neutral you would still clear over 1k-2k per month off your taxes and principal paydown.

"Hey, you can only defer money from capital gains, and not the original return of principal???  

Other times lenders may require 6 to 12 months worth of principal and interest payment.

More chances of lender recouping their principal.4.

Have complementary skillsets and spell everything out in writing.I think folks just need to understand that buying rental properties is a business small medium or large... same principals apply like what your talking about.. just because in the US our lenders allow for this aggressive leverage situations for inexperienced investors does not mean one should just go hog wild  when they start..

You want that plus 90% of the principal at the end of five years. 

If they say they will provide one, add that amount to the principal amount on the most recent statement.

I had a rental appraisal done for it for additional cost during the process and the results were good enough so that 70% of that number covered my Principal, interest and insurance and property tax payments with a little left over.