At 3.875% interest that student loan will take -- drum roll please -- over FIFTY YEARS to pay off at 100 a month.
If the interest rate is higher you'll likely die still owing money.
This website can be used to check out repayment options for loans that work like mortgages:
https://www.drcalculator.com/mortgage/As for the studio apartment rental, it's a HORRIBLE rental property investment given the numbers you present.
550 rent for a 520 mortgage? Every single day things are breaking in that apartment. Things that you will have to pay for to fix. Every.Single.Day.
You need to subtract principal and interest in the mortgage, plus taxes, plus insurance, plus the property manager, plus set aside money for repairs, plus set aside money for vacancies (because you still have to pay the other stuff), plus moneys for utilities when the tenant is gone, plus any utilities you are responsible for, etc.
You are losing your shirt, you just don't know it yet.
I don't know what you can expect to increase the rent to. But unless it's a hell of a raise in rent (like close to doubling it!), you're probably going to lose money. It's just a matter of time. The only reason to even consider keeping it is that the mortgage will be paid off in 5 years. But all those other expenses will still be there so don't count on seeing much of that 550! You still need to get the rent raised substantially.
The "1% rule" says you should be renting out the property for no less than 1,250, 1% of its cost while you still have a mortgage. While the 1% rule is no substitute for actually running the detailed cost numbers, it's a quick rule of thumb.
By way of example, I live in a low cost of living area in the US. I buy $35,000-$40,000 properties and fix them up. After repair cost takes the total property cost up to $45,000 to $50,000. I rent them out for $765 to $820 a month.
That's a 1.6% to 1.7% rental rate. 2% would be a holy grail percentage.
You're running at 0.4%. It's a money loser.
Until you learn how to find and purchase a property that will rent at least at 1% of the cost of the property, and preferably much better than that, you're going to be better off not buying.
That's my take on it.
Check out the book list in one of the sticky threads on the real estate section of the forum. Lots of good books that will tell you how to go about it! There are probably UK-oriented books that would cover similar info.