Your question is pretty vague (like what do you want to know about being financially independent?) so I will assume you just want to calculate how much you need to make.

Calculate your monthly expenses: transport, food, health, rent, utilities etc. Increase that by 5% to roughly account for inflation by the time you graduate. Now calculate how much you would need to make before income tax.

Also, make sure you are making this number on your own (don't depend on splitting expenses with gf. better safe than sorry)

In short. One house is paying itself off and both have abysmal interest rates. I think it would be wise to invest your savings. Even a 3% yearly return (very low) would be more beneficial than paying off your mortgage.

Might as well buy another rental ;)