Draft purchase agreement for undeveloped land

I received the draft purchase agreement for our reserved plot today. Is there anything specific to watch out for, since the new development area is not yet developed, but currently just a field? The plot number and size are included. What makes me a bit suspicious is the following entry under "Warranty":

"The buyer has thoroughly inspected the purchase object and buys it in the present condition, which is known to him. The actual present condition is therefore also the contractually agreed one, even if individual condition characteristics were not recognizable or later occur differently, as long as nothing else results from today’s document. This applies in particular to the plot size and a certain usability."

Does this mean that the plot size may still change during the development or whatever, and in the end we have fewer sqm than we bought??? o_O

Yes. But this is normal for plots that are yet to be surveyed; once the survey has been completed, the size will no longer change.

Did you have a soil survey carried out beforehand?

No...
Should one do that and why?

So that you have an idea of the costs that will arise when founding [eure Firma].

Ok, and do you do that before the purchase? And where do you turn to for that? How much does such an expert opinion cost?