Refer to some of the tutorials on this site about adding new frames and things, and see if you can work out how to do it after reading them.
You'll have to add in the coding to make the rifle reload after firing, too.
As for the part how you want it on the right side, i'm not sure

I'm only new aswell.
It could be something to do with the properties of the model, or something in the actual coding.. someone else will help you out,
or if you're impatient, try to find some other tutorials to do with it.