Though I doubt it will get to the size of a gigabyte, it maybe possible. I have no idea at this point really, though the art will be very detailed and will require many, many, files, as will the music. The whole point is to get the game to be as efficient as possible and as small of a file size as possible while still containing all the necessary assets for the game to come together and maintain the quality of the project vision. When I spoke of hoping to create the biggest GE game, I was referring to content primarily, though it is very likely the file size will grow rapidly as content grows.
I haven't really given much thought as to how I will go about handling the sound/ music, though I definitely do not like the idea of using .wav files because they consume so much space. With a soundtrack like the one I imagine creating, this is a horrible idea and will no doubt exponentially increase the file size to undesired levels. I'm a fairly talented musician and somewhat knowledgeable about sound so I'm not really worried about creating the soundtrack, but I am however worried about integrating it into GE somehow. I have thought about using a tracking program such as milky tracker, but the process is extremely time consuming and I would like to avoid it if at all possible. I have opened up the source code for GE (1.4 anyway, thats all that is available for Mac I believe at this point?) in Xcode a couple of times, though I can't say I entirely get it at this point, though if it is possible for me to slightly reprogram GE to accept other types of audio files in order to achieve the effect I am going for, I am definitely willing to go the extra mile to make that happen at some point. For now, I figure gameplay, programming, art and storyline are more important in precisely that order but if anyone has any suggestions on how I should go about audio, I'd appreciate it.
Yet speaking solely in term of scope, my goal is to make the central game play roughly around 60-80 hours, grinding is not something that will be necessary to progress thru the story (which will unfold in a number of many ways) but will be encouraged by giving the player an expansive and dynamic 2D world to explore and see all of. Ideally, the player will be able to explore the interior of almost every building in the game. The areas players explore won't be just pretty places to look at but, perhaps locations to acquire new equipment or materials, to meet interesting NPCs, to risk a chance encounter with an enemy, to recruit a member to your party you might have otherwise not, to explore a sub quest option, etc., I think there will be a little something for anyone who enjoys RPGs of any form to enjoy.