Pave a 100m² driveway

The terrace at my parents' was done by a professional and every year when I visit, I get to scrape out the crap with the jointing knife. As already mentioned. Comes from above.

Weeds do not come from below either but "in flight". How should weeds come through compacted gravel?

If there is dirt in the gravel...

I will remind you when the first questions come up about why the water is standing still now and the weeds are growing out of the joints.

What would happen if water stands and weeds grow out of the joints?

For the large area, I would also hire a professional. Maybe you can provide helpers and save some costs that way. Then the bill might not be quite as high.

We had 135m2 paved and paid about €4,000 more. I think you got a really good offer. I have seen the effort required for paving. I would never do it myself. And for us, everything was already compacted and excavated.

The question always remains what is included in the amount of money. The stone alone can make huge differences between €6 for hardware store paving stones and €35 for clinker pavers (and for terraces with large slabs easily up to €1200/sqm). Then it also depends on how much filling was needed. Just laying the paving stones cost us €13/sqm including prior scraping and sanding afterwards, etc... The hardest part of paving is probably the preparation. If the area is straight, laying the stones is no big deal (either the stones have automatic joint spacing or as a layman you use a joint spacer). Only getting it straight with a predetermined slope (absolutely necessary to avoid standing water) is not so easy. But all doable. As already said, it would be best to have a knowledgeable person with you.