I have been asked about this a million times. I am sorry it is so basic but it's all I really can offer. Simply do your best and use your imagination. There is no right or wrong way to create a mod, just have fun!
I think it would be helpful if you posted a guide on how to paint. I've tried my hand at painting nerf guns, but they don't come out nearly as professional as your jobs. Sometimes I hear about "dry-brushing" or "liquid mask". I'd love to learn some tips on how you paint guns.
Can you tell me exactly what type of paint you use? it looks so smooth and clean, im assuming not the typical paint, also are the guns sticky after pain dries? if so, is there a way to make it less or non sticky?
I think you've done a perfect job of enough information, even a beginner should be able to figure out how to mount and combine the pieces, learn lessons along the way, and perhaps even think of better ways or items to add. As SolTheNinja pointed out though paint color is also a hard thing to know and choose.