Answers
You just need to come to Greece at least once. Entry stamp is enough.
An entry visa, that is, legal entry in the country, is necessary to obtain a residence permit for owners of real estate property. Following the issuance of a residence permit, and for its duration, there is no need for a visa. Pursuant to Law 4251/2014, any third country citizen who has entered the country legally holding a visa of any type or entered the Country under a visa waiver regime such as American passport holder or is a legal resident of the country irrespective of their status or type of residence permit, has the right to apply for a residence permit. Your first step is to enter Greece on your passport and start the process of the Greek GV Program. Before the expiration of 90 days, you have to sign a PoA in front of a Greek Notary for the project's implementation.
It is not necessary to issue a visa D. You can just enter.