So we went to the bank this morning, where we had an appointment with a financial advisor who already knew the estate agent. (Though she didn't know about the appointment; apparently, the call centre agent with whom I talked hadn't managed to notify her about it or something.)
However, it turned out that financing that particular flat would cost us about 20% more a month than we had budgeted; or, conversely, that with our budgeted monthly rate we would (just barely) be able to pay for the flat itself but not for any of the "extras" (mandatory parking space, real estate purchase tax, notary fees, renovation costs, possibly one or two things I've forgotten).
Stella is going to think about it again tonight and look over our finances, but I suspect that unless my income changes markedly, we're not going to be able to afford something with those costs.
Still, it was useful to know how much we would be able to finance at a given monthly rate, and also because she said they would also cover notary fees, estate agent's commission (none in this case), and similar costs, something which Stella had thought bank loans typically didn't cover (that they would pay only for the cost of the house or flat itself and possible some renovation work, but no other fees).