Purchase contract for property, down payment

Hello everyone,
we are about to complete the purchase of a plot of land. However, we would like to pay for the plot in 2 installments. The first about 60% now and the last at the end of the year. The reason is that we would like to "secure" the plot and did not want to take out a loan since the remaining amount would be available interest-free at the end of the year.
The question now is, does that make sense? How does it work with ownership? You can only start building once it is fully paid, right? How is access to the plot for the planner, architect, etc.?
In the draft purchase contract, the area is stated as an approximate figure, but the price is exact based on the area we want to have measured. The exact survey will provide the precise result, whereby additional area must be paid for afterwards, but a shortfall does not need to be compensated...?!
Thanks and best regards

The question now is, does that make sense?

What does the seller say about this idea?

The question is simply, does the seller agree to that?

If not, you don't even need to think about it.

Just take out a loan for the 40% with the option to repay it in full immediately at the end of the year if you have the money, that should be the easiest and you will be registered in the land register immediately and everything is done.

The seller would participate, is a private individual and quite approachable.

Seek bridge financing. A good house bank is also suitable for bridge financing without a land charge, provided the amounts are not very high and the account has been managed solidly so far.

The seller would agree, is a private person and quite approachable.

Well then I don't understand the question. Something like that is a homework assignment for your notary. Purchase price payment in 2 installments at 2 dates.

I just don't know how the transfer of ownership in the land register works. I think after full payment. But the notary knows that too.