The idea of the game is a fantasy/scifi shooter game set in some sort of dream like world, scifi tech base, alien hive, hell or whatever. There isn't going to be much of a story. The gameplay, etc will be the more important. /-- The story is this:"Lots of evil monsters attack. Only one person can fight back."
It's the human base mesh with the gun. Well, two of them.. The smaller is realistic size weapon. The bigger is not so realistic size, but realistic size weapons are very tiny when seen in the game world.
Well, realistic size humans are kinda tiny too, which would make the hitboxes annoyingly small.. Now this character would fill a hitbox with 60 unit height and 16 unit width. In games characters are usually the same height, but double the width.
So, I could make the muscles really big or make it wear some huge bulky power armor... or a bit of both...