Can I ask three questions:
a) What sort of business are you thinking of buying?
b) Would the clients be Greeks or foreigners?
c) Do you have experience of running a business at all?
If your clients will be foreigners you may be able to get away with little Greek.
You will definitely need a good solicitor and accountant. You'll probably also someone to act as a general translator when needed. This could be many days a month at first.
There is a LOT of bureaocracy in Greece compared to the UK where running a small business is relatively free of red tape.