How much would I pay in interest?

Interest rates are determined by the borrowing rate, as determined by the supply and demand ratio of the asset.

When do I need to pay back the loan?

The loan is perpetual, so there is no fixed time period. The factor depends entirely on whether your position is safe. This allows users to borrow for an undefined period of time. As time passes, accrued interest grows and could affect your health factor value, which may put your assets at risk of becoming liquidated.

How do I pay back the loan?

Please review the instructions located here.