Is this financing feasible?

Hello everyone, I have been dealing with the topic of buying/building a house for about 2 years now and have also been active here for a while.

Since there was no existing property that suited us, building almost exclusively remains an option. It was originally planned with a cheaper plot of land, but unfortunately this is not available either. Now a more expensive plot is an option, although I am financially rather skeptical.

Here are the facts:

My income: €2,650 (company car costs already deducted)
My girlfriend's income: €1,850

Total thus €4,500

Equity:
Me: €93,000
Her: €12,000

Building savings contract she: €8,000

Riester pension (whether it makes sense to include it in the financing is still questionable):
Me: €8,000
Her: €7,000

If you really scrape everything together now, I come to €128,000 (incl. Riester). But then everything is really included and no reserves remain.

The plot of land in question now costs €120,000.

We have spoken with a few prefab house providers so far and the shortlist includes Schwörerhaus and Fingerhaus.
House costs for approx. 130 sqm of living space are about €260,000.

If I add it up now:

Land: €120,000
House: €260,000
Selections: €10,000
Floor coverings: €10,000
Outdoor facilities: €10,000
Additional building costs: €40,000

Total: €450,000

If I were to deduct all equity (which of course is not possible), I would be at €322,000. Let’s say I keep €17,000 as a buffer, I would be at a financing of €340,000. Although I also fear that the €17k would not be enough as a reserve for building a house?
Oh yes, I am 32 and my girlfriend 26. Children are planned in 3-5 years. And that is exactly where I see the snag. At the moment we could manage a rate of €1,800, I would have no concerns there, we also keep a household budget. But how will it look with children then...
My idea would be to pay off €1,800 for the first 3-5 years and then, when the child(ren) arrive, reduce it to €1,000-1,100 and then be done after a total of 30 years.

How would you evaluate this?

Best regards,
MSPler

1,800 euro instalment is already a big deal. I hardly know any financings here that are similarly high, mostly they are around 1,200 euro.

You forgot the incidental purchase costs for the land.
There’s another 12-15K on top of that.

For 10,000 outdoor facilities you might get a lawn, above that it gets tight.
Garage or carport?
What does the land look like? Sometimes there are also hidden 20K earthworks.

Which region?

All in all, a tight case.

The €1,800 is only for the time when there are no children yet, and with our income of €4,500, as I said, I have no concerns about that. The higher rate is only supposed to be maintained for 3-5 years to then come down to about €1,000-1,100.
The additional costs for the land are correct, of course, although at least no realtor fees will be added, "only" notary and land registry fees of about 5%. The area is near Würzburg (Bavaria).
I understand that the outdoor area for €10,000 is only the bare minimum... everything else can come later. The same probably applies to the carport or garage; that will not be included in the budget at the beginning.
I do not yet have a soil survey, so I cannot estimate the earthworks yet. At least the land is flat.
I also have the feeling that it will be tight and will, if in doubt, prefer to discard it rather than push it through by hook or by crook.

In sales, you will surely occasionally have a good commission that is not included in your calculation, right? You can then use it in the first years to make special repayments, which allows you to prepare for the years with children. And in 3-5 years, the salary should also increase somewhat.

In sales, you will surely have a good commission from time to time that is not included in your calculation, right? You can then use it in the first few years to make special repayments, which can help you prepare for the years with children.

And in 3-5 years, the salary should also increase somewhat.

Exactly, but I have not included this in my calculations and want to deliberately leave it out. The same goes for holiday and Christmas bonuses. The above-mentioned amount is the fixed income. A salary increase is to be expected, but here too I prefer to calculate with the current figures.

350k * 5% annuity = €17,500 p.a. respectively ~1,460 p.m. I still find that acceptable with 4.5k, even with children, a car is already included and commissions are common. As long as the cost side is complete, I find that okay. Household budget checked? What is paid for rent?