"Hello and thank you!"
Translation:Γεια σας και ευχαριστώ!
"Γεια σας και σε ευχαριστώ!" is a bit misleading, as the "σας" and "σε" refer to different "you"s.
I agree with wchargin. The above sentence should be: Γεια σας και σας ευχαριστώ!
No, you can't from English, which is why both are (or should be) accepted. If you find that either option is missing, report it.
χαιρετε is mostly used when speaking, rarely used when writing but in my opinion, it should be accepted. Either way you can use it and it is 100% correct
Is the suggested sentence valid, it looks cropped to me: "Γεια και σε ευχαριστώ"
It's correct. You don't have to use σου after γεια. You can even say 'γεια και ευχαριστώ' but bear in mind that this specifically sounds informal and it better not be used when you refer to someone as 'σας'. So, say it to one person or many people in an informal setting, but include at least one 'σας' in formal settings, e.g. 'Γεια σας και ευχαριστώ'. :)
it is a bit complicated because in english they are both referred to as 'you'. 'σου' refers to one person but 'σας' refers to a larger group of people. Hope this helps, feel free to ask anything else, I am greek and I feel like I can give you the correct answer. Also, bear in mind that 'γεαι' is not valid, the correct answer is 'γεια' = ya, meaning hello