But a refi would be much more hassle than putting it on a credit card or financing with the contractors.

Based on this new rental what is a reasonable amount to raise the rent without scaring off the current trouble free tenants?

They usually carry a much lower interest rate than credit cards but somewhat higher than bank loans for a specific amount and purchase.

NOW, having said that, I've been told there are steps you can take to combat the issue that arises from the "gift" stipulation...First, the "gift" (loan) coming from a family member raises far less red flags than does a gift coming from a friend. 

As one client put it, "In California, tenants pay their bills in the following order: car payment, credit cards and, if they have leftover funds, the rent."

If it's $400/year per property, why not deal with it and raise the rent $35/month to cover the cost?

True, refinancing cash out will be more time consuming and costly and will raise your overall interest rate on your first lien position.

I have read the ABCs of REI and Commercial real estate for Dummies and they are both very informative books that teach all of the numbers but lack market research techniques and raising capital for the down payment. 

When renewal comes around raise the rent to account for future servicing of the septic system if it cost $400 to pump and you plan on doing it every three years raise the rent  by $11.50 to cover that cost.

I am from Dallas and was raised there.