I don’t want to start a childish discussion now, but I find it absurd to park a one-year-old child who has just taken their first steps for 30-40 hours per week in a daycare. Children like to sleep 12-13 hours at night, meaning the child spends 50% of their time in a daycare center. Sure, the child is not treated badly there, but I wouldn’t buy a dog just to put it in a kennel again. All this just so that you can afford a home of your own. Children want time with their parents, not a €30k kitchen with high-gloss fronts.
To the actual topic: From my own experience: The customization will always cause additional costs. The extra repayments mostly go towards other things. The intention that you always dutifully make your extra repayments is about as likely as saying after the dentist, “from now on, I will use dental floss daily.” Returning to work 6 months after birth is certainly possible, but I wouldn’t firmly plan on it. Two full-time jobs with 1-2 children, I consider suicide. If you find childcare, children are often sick and depending on the daycare/kindergarten, children often have to stay home even with a runny nose. But even if all children are cared for, it is a mammoth task.
All in all, I would therefore not deviate from the project. You still have family in the area etc. So it will certainly not be as comfortable as you have currently calculated, but certainly doable. Life usually turns out differently than you think.