Well, I would still make sure that in 4 years not €35,000 but the mentioned €40,000 is available. Otherwise, there will be a new loan. Actually, I would even have the roof done right before moving in. I don’t know the year of construction and other details, but new insulation could save you a lot on heating costs, even if it’s only for 4 years. And later you simply won’t have any trouble with it once you already live there.
Anyway. There are general rules of thumb that say you can usually afford a loan up to 100 times your monthly net income. The exact factor is debatable, as well as how current interest rates play into it. But you yourselves are well below that limit even without the maintenance payments. So all good. And because you are so far below the rule-of-thumb limit, I wouldn’t choose an expensive full-coverage financing option with a home savings contract or something similar, but simply a classic annuity loan with a 15-year fixed interest rate. The cheapest one, basically.