The developer requires a down payment to start drawing

You have to pay it anyway. Whether as a down payment and then less as the remainder, or a small down payment and a lot at the end, it ultimately doesn't matter :)

For a detailed offer, a clear cost breakdown, the construction service description, as well as reasonable floor plans that one can work with are needed. These tasks are clearly sales tasks for acquisition.

What if the guy only delivers junk? Then the money is gone for nothing and nothing again. If you realize that after 1-3 appointments everything is going in the right direction, you can talk about further planning and costs. But in this way, you bear the sole risk, he can present whatever he wants to you, the money is already secured.

That would be an absolute exclusion criterion for me. We also talked to 6-7 companies, and if we realized it wouldn’t work out, we didn’t waste anyone’s time and canceled after the first appointment.

If you purchased the property separately from the city, then it is not a developer from whom you always acquire house and land as a unit. You also do not own the land until the completion of the overall project. What you mean is a general contractor or general purchaser. For such a planning fee, I would expect more than 8 hours of drawing by a technical draftsman. This would include intensive (several hours long) planning meetings, multiple rounds, and different planning variants.

Prepayment for an unknown service? Hands off.

You have to pay it anyway. Whether as a down payment and then less as the remainder, or a small down payment and a lot at the end, it doesn't really matter anyway :)

Do you handle your money so casually as well?

GU is fully booked and does not need the contract. If there is a choice, inquire with other GUs.