I have read somewhere is 30%,I'm not sure if i'm able to pay more than that.
This is a question your notary or lawyer will be able to answer definitively.
Can anyone confirm if the notary's fees are fixed according to the land value or varies from one to another?
Yes, notarial fees are calculated based on the value of the land/property, but can be negotiated down. The PCC tax of 2% applies to the value declared on the notarial deed.
I've read elsewhere that notary will ask from the vendor to prove the ownership,am I wrong?
The notary is responsible for getting an up to date copy of the land registry document for the property and checking that the person selling the property actually has the right to sell the property based on what it says there (otherwise the contract is void and you have grounds to sue the notary).
At the completion day,the notary will ask the vendor to present a letter from the local council stating that there are no outstanding loans, debts or mortgages on the property.
can anyone confirm please.
This is something you can stipulate that is included in the contract but you should check with a lawyer what other things you should be asking for.
What is the maximum period between the preliminary contract and the completion day?
It's up to you and the vendor.
the guy owned 5 plots,sold 2 already,he provided us with local authorities planning permission related to the plot.
Is this a WZiZT or a Pozwolenie na Budowe. Anyone can apply for the former, whether or not they own the land or have any rights to it. However, only someone with legal title to the land can apply/be granted the latter. If you have the latter, make sure that the contract explicity states that that the vendor is signing over the rights to the land to the person buying it.
Look, I know what you're trying to do here but your deal isn't run of the mill and you really should invest the few hundred quid or so to get a good lawyer to work for you and protect your interests. Unravelling problems to do with property transactions is an expensive and lengthy process.