140k of federal loans after getting my BSN

I’m a new grad nurse and I’m currently about $140k in student loan debt, all federal loans. I still live at home, so I don’t really have major expenses besides gas and personal spending. I’m starting work in July, and my plan is to aggressively pay these loans down by putting around 85–90% of each paycheck toward them.

My starting salary will probably be around $80k, and I also plan on picking up extra shifts when I can to increase my income. My goal is to have the loans paid off within 5 years if possible.

I’ve also been thinking about refinancing to get a lower interest rate. Since I’ll have a strong cosigner eventually, I was considering waiting about 6 months after starting my job so I can show stable income before refinancing.

What I’m unsure about is how to refinance strategically. Would it make more sense to:

refinance smaller chunks at a time (like $20k portions),
aggressively pay one refinanced loan off first, then refinance another

or refinance a larger amount all at once since my goal is to pay off as soon as possible

also wondering since I want to do the avalanche method and I want to pay off highest student loans rates first, would that mean still put all the extra money to federal since it would be higher and then pay the minimum/normal amount for the refinance portion??

I’m trying to balance getting a lower interest rate while also keeping some flexibility/safety since federal loans have protections that private loans don’t.

Has anyone here paid off a large amount of nursing school debt this aggressively? What strategy worked best for you?