We have offers for about €70 per m² for flooring (vinyl, fully glued down, with leveling compound and skirting boards).
If you install click vinyl yourself, including impact sound insulation, you can probably get it for €20-25 plus skirting boards plus your own labor.
That is certainly possible, but then €5-6k is already gone just for the floor.
The budget is definitely not enough for parquet!
For the rest, buying wallpaper + paint and doing it yourself is probably possible too.
But then no craftsmen must be paid.
There is plenty of price information here in the forum for painting work.
If you have everything done with parquet flooring, walls skimmed with Q3 + fiber fleece + paint etc., you’re looking rather at €35-50k depending on material prices.
Just get quotes for the trades separately, then you will have certainty. Call a painter on Monday, send an email with measurements.
Do the same for the floor. Then you can still apply the red pen.