Buy-to-Let lending differs from normal residential mortgages. On the whole the lender will require a bigger deposit to reduce the risk they are exposed to and or charge a higher interest rate than normal. Remember rental income is not guaranteed so the lender wants the extra security of a lower loan to value. (LTV)
As a rule of thumb lenders will want the rental income to equate to 125 or 130% of the mortgage monthly payment. E.g. £68,000 loan, property value £80,000, interest rate 6.5%. In this case rental income would need to be £482.25 per month, which would be 130% of the mortgage payment of £370.96.

The maximum number of properties that Buy-to Let lenders will allow you to use as security varies from lender to lender. Some will only lend on one whereas others have no limit. Also the type of income considered varies, some take only rental while others use rental plus earned.
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