Factors impacting ability to take out more loans for investments

[John Y.]

I'm thinking of buying more rental properties and curious to factors that may limit ability to get more loans. I've been borrowing under my person and not my LLC .

-I have two loans ($500K total) on two properties, taken out as investment properties under my name (not LLC)

- Both properties more than cover loans and slight positive cash flow each month.

Q: Is there a debt to income or some ratio that lenders look at when determining whether if I hit some ratio that will cause them to stop lending to me? Or as long as I can show I have income to support service of those existing loans, then I should be able to get additional loans to buy more properties. 

Q: If I get a commercial loan, they are usually 5 year ARMs and I don't want to want to deal with refinancing. Does it make sense to do commercial loan or just to personal investment property loan? What are pluses and minuses to each?

I apologize in advance if its not phrased clearly and I hope you understand the jest of the question.

Thanks in advance.

John