1) Do you work for a nonprofit or gov agency where you can look into PSLF 10 year loan forgiveness with no tax hit at the end?
2) yes, 401k savings is very important at your age with little savings. But if your income is high enough to pay off 200k in 4 years, you probably can do both by paying off loans over more than 4 year but less than 15. What’s your retirement goal? Knowing your target amount and date will help you decide which route to go.
3) payments are 10 or 15% (depending on the plan) of your AGI - 150% of your states poverty line for your family size. Yes, contributing to 401k will lower your AGI and your payments.
4) There is no way to get around having to do the maths on forgiveness vs paying it off. Use the studentloan.gov repayment estimator to see how much you’ll have paid over 25 years and use the estimated amount forgiven to calculate what your tax hit will be at the end.
https://studentloans.gov/myDirectLoan/repaymentEstimator Compare that to how much you will pay if you pay it off in four years. It might be less to just pay it off. Alternatively, how does the income based total amount paid (with tax hit) compare to switching to a 10 year plan? Can you afford the 10 year plan payments and max out your 401k? Then you would be done with the SL payments in ten years and not worry about the tax consequences.