Home calculation - realistic?

Hello everyone,

We, that is me (30) and my wife (30), have decided to move into our own house sometime (in 2-3 years).

We have now relatively quickly won a nice plot of land in a new development area in Northern Bavaria and reserved it.
We have been reading for a while on many websites and are dealing with our financial possibilities.
We would like to have your assessment of whether this is realistic.
We are planning with about 550,000 euros (maximum, preferably less) and think about dividing it as follows:

Plot including additional costs 95,000 (fixed)
House ~330,000
Additional costs ~50,000
Garage ~20,000
Outdoor facilities (564sqm plot) ~25,000
Interior furnishings ~25,000
Kitchen ~10,000
We imagine 140-150 sqm, possibly in the city villa style, prefabricated house without a basement. Whether solid or timber frame then depends on the respective offer situation.
As own contribution (family) we could possibly do painting, parquet, tiles, and installing the sanitary fixtures, for example.

Thank you very much for your answers ☺️

Financing stands?

Is the financing secured?

We have a concrete offer, yes.

It is not signed yet, but it should be fine.

Setting the sanitary fixtures will be difficult to do in EL with a developer. We have also asked several about it, but it was always said that we would then have to do the entire piping. But you can always ask. Painting, flooring, and tiling sounds good. You can save a lot of money if you spend the weekends on it. Outdoor facilities sound good. But it can also be done with significantly less. Interior design also seems like a lot to me, but everyone has to decide that for themselves. I find the kitchen way too little because you have so much in the other two items. Of course, 10k is definitely sufficient and doable, but since you have so much in the other posts, it just looks odd. Otherwise, the costs definitely look realistic. You should still plan a buffer of 10-20k.

Looks doable at first glance.
Garage has a buffer (to do later)
Interior design budget is enough for many rooms if you don’t fall in love with special pieces of furniture.
Kitchen budget is feasible with a decent kitchen without frills.

How high are the development costs?
Are there any special features of the terrain that would increase construction costs (slope, soil conditions, flood area, access road...)?
Who owns the access roads / Is there an owner participation in road repairs (bad surprise)?

We are planning with about 550,000 euros (maximum, preferably less) and think of dividing it as follows:

Land including additional costs 95,000 (fixed)
House ~330,000
Additional costs ~50,000
Garage ~20,000
Outdoor facilities (564sqm plot) ~25,000
Interior design ~25,000
Kitchen ~10,000
We imagine 140-150sqm, possibly in city villa style, prefabricated house without a basement.

Very realistic, the calculation. At least these are prices from today. Whether they still apply in 2020, I doubt. I have two objections. First, the mentioned prefabricated house. Then the base slab could be added to the targeted 330,000 calculatively. Second would be the special equipment, which does not fail to appear, such as more sockets, etc. That's how it is. However, the item interior design is flexible and does not have to be invested immediately into the house, so it could serve as a buffer.

Installing the sanitary fixtures will be difficult to do in EL with a developer.

I don't read anything about a developer. But yes, with a "turnkey offer" that is difficult. But self-installing barely saves anything unless you want to really sink money at Reuter and co. instead of the offered average equipment from the builder.