Is financing the construction of a single-family house of about 130 sqm realistic?

Our data. I hope I have entered everything correctly.

General information about you:

[*]How old are you?
35/36
[*]Do you have children?
Yes, one. 1.5 years old.
[*]Are children planned?
Yes, two.
[*]What do you do professionally?
Engineer, industrial clerk
[*]Are you employed, self-employed, retired, housewife, househusband, etc.?
Employed
[*]How many hours do you work?
40h/16h

Income and asset situation:

[*]What income do you have (gross/net)?
4000€ net he (without Christmas and holiday bonuses)
1300€ net she
[*]How much child benefit do you receive?
250€
[*]How much equity do you have?
155,000 Euro and
215,000 Euro existing loan with 1% repayment + 2% interest (total 640 Euro) - remaining term 20 years. I am aware that the 215,000 Euro is not equity, but I didn’t know where else to put it.
[*]How much equity do you want to invest in the house project?
All

Expense situation:

Housing costs:

[*]current cold rent
600 Euro
[*]current warm rent
1500 Euro (costs of existing loan already included (640 Euro monthly))
[*]electricity
60 Euro
[*]water, sewage, garbage fees, street cleaning
67 Euro
[*]telephone, internet, mobile phone
50 Euro

Mobility costs:

[*]savings rate for new car
75 Euro
[*]insurance
84 Euro
[*]taxes
25 Euro
[*]fuel
100 Euro
[*]repairs
75 Euro
[*]Is there a second car, motorcycle, scooter? Please provide all items again!
Information for both cars combined

Insurance costs:

[*]liability insurance (including animals)
6.50 Euro
[*]capital or risk life insurance
35 Euro
[*]pension insurance + retirement provision (including Riester, Rürup, etc.)
520 Euro
[*]disability insurance
120 Euro
[*]accident insurance
11 Euro
[*]household insurance
8.50 Euro

Living expenses:

[*]groceries
600 Euro
[*]restaurant costs
100 Euro
[*]care/drugstore
100 Euro
[*]pets (food, vet, medicine, stall costs)
15 Euro
[*]medicines
5 Euro
[*]clothing
75 Euro
[*]furniture
-
[*]daycare/school fees (and meal money)
160 Euro
[*]club fees/gym
30 Euro
[*]toys
15 Euro
[*]TV/video/audio/CDs/DVD
35 Euro for Spotify, GEZ, and Netflix

Savings:

[*]vacation
400 Euro
[*]house
300 Euro
[*]hobbies/gifts
300 Euro pocket money
[*]other
30 Euro child savings

Other expenses:

[*]loans?
640 Euro

Income and expense totals:

[*]total income
6300 Euro incl. Christmas and holiday bonuses, tax refunds, child benefit
[*]total expenses
4900 Euro
[*]balance
1400
[*]of which sum cold rent and dispensable savings (e.g. savings rate for house)
300 Euro + 600 Euro = 900 Euro

General information about the property:

[*]How big is the plot?
840 sqm
[*]What are the dimensions?
12*70
[*]What is the standard land value?
160 Euro
[*]New build, old building (year built), house type?
New build
[*]Garages?
none
[*]How big is the house? (living area / usable area)
130 sqm / 160 sqm
[*]What is the market value of the plot and house after completion?
approx. 620,000 Euro

Construction or purchase costs:

[*]plot costs
85,000 Euro (already paid)
[*]development/earthworks
15,000
[*]acquisition incidental costs (notary, court, property transfer tax, broker)
1,200 Euro
[*]construction or purchase costs (incl. architect, structural engineer)
470,000 Euro
[*]additional construction costs (e.g. house connections, soil surveyor, construction power, etc.)
20,000 Euro
[*]outdoor facilities/terrace, paths, garden design, fences, etc.
10,000 Euro
[*]financing costs (e.g. fees or commitment interest)
12,000 Euro for interim financing for the 215,000 Euro to be taken over (can only be transferred after completion).
[*]total costs
615,000 Euro incl. plot

Other costs:

[*]kitchen costs
20,000 Euro
[*]photovoltaics
20,000 Euro
[*]furniture, lamps, decoration
2000 Euro for new desks/otherwise all other furniture taken over

What do you think, is this realistically feasible in our situation right now?

Let's calculate backwards. Costs / other costs: approx. 660k less equity: 155k less paid property: 85k Financing amount: 420k Financing component 1: 215k loan assumption for 640€ monthly. Financing component 2: 205k at 5.5% annuity for 940€ monthly. ==> Total financing costs 1,580€ with income > 6,000€ ==> If you don't manage that, then you have an expense problem, not an income problem I hope I understood the numbers correctly. Whether an immediate photovoltaic system for 20k is necessary or if 10k for outdoor facilities (driveway, house access, terrace, plants/lawn, fence) etc. fits, I cannot assess. It also depends on the property what exactly the earthworks will cost. Overall, however, roughly plausibly calculated.