GDPR compliance for possible new start up business

Answer:

Based on the information you provide is quite unlikely that I can provide an accurate answer. The following factors need to be considered before providing you with an informed answer:

Which is the source of collection of the personal data?
Which is your legal basis for processing?
Why was the personal data collected and for what purpose?
What will be the purpose of selling the database?

This minimum amount of information is required before attempting to provide any advice.

how much will a short consultation be with you?