I was thinking of doing voice overs (that I will upload to OGA ofc). What's the rule on swearing, and is there any difference between audio and text. And is there a line. Eg The story I'm writing has something bad happen and the character would like to yell Shi*!  

Although not encouraged, coarse language is OK in audio or text or both.   Just please put a notice or warning somewhere in the game description so folks know to be careful about playing the game around children (eg. their kids).