Finance property - take a loan to secure the interest rate?

Hello,
my name is Jan, I am 32 years old and would like to build in the near future.
We can also acquire a plot of land. For that, we need to raise approximately €90,000. The building area is not yet developed. So it will take some time after the purchase before we can start building. We could pay for the plot of land from our equity.
My question now is whether it might make sense to already take out a loan for the plot to secure the very low interest rates and then invest the equity later into the house?
Or are the administrative costs too high if we basically have to take out loans at two different times? And do we perhaps limit our flexibility for later negotiations?

Which administrative costs?

No idea, registration in the land register?

You register a land charge once, done

It makes no sense to pay interest now, although no interest has to be paid if equity is used.
Also, yes, you are now committing yourself to a bank in the first rank in the land register; no other bank will gladly enter the second rank. This means: bite the bullet with the first bank, later have an expensive deal, or bring a second bank on board under poor conditions, if an offer comes at all.
This already disproves your calculation if interest rates are supposed to rise somewhat. But that is not certain, so you will be in a better position by using equity now.

Unfortunately, we did it that way. Low interest rates - financed the land - saved equity for the house. It worked well for us, but you are tied to the bank that financed the land (first priority land charge). You are more independent if there is no land charge entry yet. And you can't always get out of the contract by paying a prepayment penalty (depends on the bank and what is stated in the contract). The land also counts as equity.