"Goodbye = ahndeeo "
True, but you would normally only say it if you were going away (e.g. at the end of your holiday)
Yeia sou (singular) or Yeia sas (plural/respectful) are normally used for both hello and goodbye. You can also shorten it to just Yeia which is equivalent to Hi
Kali spera is used in the evening when arriving, kalo vrathi when leaving. Kali nichta is usually used when it's late late enough to assume that the evening is over and the next stop is bed...
You may also find Poso kani (how much does it cost?) useful.