Where exactly should I use "shall"/other tense in this agreement?

Where exactly should I use "shall"/other tense in this agreement?

In "legalese", including in this loan agreement, "shall" is the preferred modal verb to refer to the future. Replace "shall" with "will" as you read and the meaning might become clearer.
For example, clause 3 says, "The borrower is obligated to pay back the loan..." while clause 4 says, "The borrower shall be obligated, if..., to pay a default interest rate." This means as soon as this agreement is signed, the borrower immediately is obligated to repay the money by the deadline, and the lender will have to pay interest only after the borrower doesn't pay it back.
(Incidentally, it makes no sense to me why a lender would have to pay interest if the borrower doesn't repay, but I'm no lawyer)