mobile internet stick questions?

going overseas and im bringing my laptop and im getting a mobile internet stick to use internet there
so i wanted to know if i buy them here will they work overseas?
can i get one where i pay once and then when i use all of it then is that it ? or does it have to be a monthly payment? because i just wanted to use it for a month then not use it ever again when its out of internet

and how many gbs should i get if i would use it around a few hours a day (or less) and just on facebook, msn etc etc, and watch a few videos every few days and webcam a bit. and need it for at least 4 weeks

im really clueless about these things
 
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