How can I verify the minimum monthly payment number and how it breaks down into principal vs. interest if all I know is the current balance and interest rate?
How can I determine the payoff date of that loan?
1 is pretty easy.
Interest for a month can be calculated by taking your whole interest rate dividing it by 12 and applying it to your balance.
for 2 you can use amortization schedules or your can just go to this Existing Loan Calculator which makes it easy for you to compare what adding a few extra dollars to your payment will do to your pay off date.