Weapon Upgrades

Hello so for my gamemode i got a idea making Upgradeable weapons

what i want to do is attach a model to a weapon bone lets say the middle bone so i can attach diferent iron sights to it
and also be able to alter a weapon value at real time such as max ammo count etc

so since im a bit new to lua i did a bit of research but founded nothing so any help is very appreciated!

Might use this as a reference, http://www.facepunch.com/threads/1060381-Customizable-Weaponry.

Might want to use the Swep Construction Kit thingy to put models on v_models of weapons.

And check to display certain models.