ok, let's see....thank you is 'multumesc' or merci (I know is the french word but it's the accepted form for informal talk).
"Hello" is "buna ziua" which actually means "good day" and depending on the time of the day you can say "buna dimineata" (good morning), "buna ziua" (good day) or "buna seara" (good evening). usually "buna ziua" can be used through out the day, starting with 10 Am or so until 5-5 30 PM. In informal version would be "Buna." used for any time of the day.
"Hello, brother, long time no see" can be translated to "Buna ziua/seara, frate, nu ne-am mai vazut de mult." or "bine te-am gasit, frate, nu ne-am mai vazut de ceva timp." (well find you, brother, we haven't seen eachother in some time.)
Maybe the guys here have some other ideas...
Feel free to PM if you like.