Payment plan set up strangely?

Good day dear community, I am David, 31 years old and from Viersen. My wife and I want to build this year and have already set almost everything in motion, except for the signature. The reason is the payment schedule of the contractor. We are already a skeptical family when it comes to a lot of money. The thing is that an old building is supposed to be demolished and four new buildings erected. According to the realtor, the demolition is supposed to take place in April/May 2019, but there is nothing in black and white. So it will be a partition transaction between four builders. Could you give us your opinion?

What exactly does the "contractor" offer?
Who owns the plot of land on which the houses will be built?
What statements has the building authority made regarding demolition and land development?
The payment plan itself seems OK. It just has to be certain that construction can basically proceed before sinking money into the planning.

What exactly does the “entrepreneur” offer?
Who owns the land on which the houses will be built?
What statements has the building authority made regarding demolition and land development?
The payment plan itself seems OK. It just has to be certain in principle that construction can take place before you invest money in the planning.

Hoihoi,
I probably gave too little information^^

The land itself belongs to an independent seller. The realtor receives a commission on the land and a commission from the construction company.
We have nothing in writing from the building authority.
We have received a "building encumbrance report" and a "neighboring party certificate."

I see 2 reasonable options - that does not mean there are more:

1.: Clarify conditions yourself. Preliminary talks with the building authority, if OK, then buy the plot and award the contract for the house construction. (Construction company or self-awarding with architect and local craftsmen)
2.: Construction company clarifies conditions, purchase of the plot and construction contract are linked to the feasibility of the project.

The risk of signing a construction contract without knowing when, how, or if construction can take place at all, I, even as a hopeless optimist, would not want to bear.

Strange design, but that may also be due to the type of business. Above all, the first and the last installment would bother me. I am also not sure whether the 3% final installment is still even permitted under current legal regulations.

2.: Contractor clarifies conditions, property purchase and construction contract are linked to the feasibility of the project.

We have chosen this option! We told the real estate agent and the contractor that we need a concrete plan for the bank and would like a "draft construction contract" in advance. It is supposed to happen this week...

But as you already said regarding the contractor's payment schedule, everything is OK? Also that you pay a large amount in advance and haven't even started any preliminary work?

Is that normal?