question on rental refinance and big picture game plan

[Jeffrey Vlk]

Greeting everyone! I remember reading Rich Dad Poor Dad and getting hooked to start investing in real estate. I joined the military and married/had kids young which is not a good situation financialy when trying to find money to buy rentals. My goal was to move into a house paying owner occupied rates, move out in a year, and then rent it out. I acquired 3 rentals this way and just got tired of putting my family through moving so often. My goal is still the same from years ago; be able to support my lifestyle with passive real estate income. My questions are as follows:

1. I own a condo that has 23 years left on the loan, 4.625% rate with $102,000 left on loan and also another rental with 23 years left on it at a 4.0 % rate and $169,000 left on it (sold the 3rd rental a year ago). I know the name of the game in rentals is cash flow..should I refi these back to a 30 year to increase my cashflow since I am only making about $350 a month between the two now or should I not refi since I have already been paying for 7 years and shouldn’t go back to a 30 year. 

2. What do you think is better...buying a bunch of houses and let the renters pay them off or hit a certain number of houses say 10 and then start paying them all off? 

Thanks for the help