Sorted:

Burrowing money in a currency then the exchange rate increases

Borrowing money from an exchange company and keeping it there until the exchange rate goes up then exchanging it

Debt does not exempt one from Zakaat

Returning burrowed money in the same currency with increase in exchange rate

Riba is from the Major Sins – Tafsīr Suratl-Baqarah by Ibn Kathīr

Does A lender requesting a service from a lendee enter into Usury?

Paying back debts from harām after repentance

Is taking the down payment permissible?

Repaying a loan when the creditor is not traceable