How soon can I refinance?

[Vee Vu]

Hi everyone. I'm planning to buy rental properties in Baltimore, MD and nearby areas. And I really concern about the refinancing, because my capital is limited. I have a few questions:

1) How soon can I refinance after renting out the property? 

2) Will any lenders/ banks let me refinance based on only the rental income of the house? (I don't have a job now). I really appreciate if I can receive some referrals to those lenders/banks. 

3) How to add more value to a property which is bought at the market value? Are there any ways to make sure the appraisal for the refinancing will come at a higher value than the purchase price?

Thank you!