Doesn't the senior most debt agreement carry the most restrictive covenants, hence if complying with those covenants we should not worry about the other agreements?

Seniority is typically based on the sequence of liens on assets or collateral held, more that covenants, although senior debt covenants will usually require specific subordination clauses in junior debt agreements or preclude issuance of such debt. Senior debt agreements drive the language of junior agreements as a condition for permitting additional debt. The amount of additional debt is almost always limited, with additional covenant requirements regarding defined capitalization ratios and interest coverage ratios.

It all depends. Junior debt that was written at a different time than your senior debt under different credit market conditions with the company's credit standing being different can have permitted baskets or ratios stronger than the senior credit. Also, there may be covenants peculiar to that type of agreement. Also, the non-financial covenants can easily be different.

It depends on the cos credit and when the debt is issued. If senior and sub debt are issued together, the senior will usually have more restrictive terms/covenants. If sub debt is placed on after the senior, it will probably be more restrictve due to higher risk and more demands by sub issuer.

The senior debt does not necessarily carry the most restrictive covenants. The previous responders have explained that well. You should address, project and monitor each of the lenders' covenants as distinct debt service issues. Often, failure of one lender's covenants will trigger a default in other debt, even if that covenant did not appear on the other lender's loan agreement. Be safe -- treat them separately and meet them all if you can.