There are no guidelines for n00bs and being a n00b is not a bad thing, it's just a label
The project is ambitious as Gun Freak said, if you have the woodworking skills it is definitely possible. I did notice that you didn't mention the valve or loading mechanism (in terms of how the projectile is stripped from the cartridge, fed in to the barrel, and isolated from the cartridge).
I would forget about the silencer and your fancy projectile for the time being, you can work those out later. Though, decide now if you're using spherical projectiles or 'long-body' projectiles. If you know this already, do you know exactly the ammo you plan to use?
The loading mech. shouldn't be too hard, I'm picturing a Z-shaped magazine spring to push the projectiles up and a bolt-action mechanism that opens the breach, allows a single projectile to be loaded in to the barrel, and isolates the cartridge when closed. While this sounds simple in concept, no doubt you'll be spending hours with a file trying to find any obstructions that are preventing the projectiles from loading smoothly.
The valve could be difficult as well, depending on how you want it and what projectiles you use. If your projectiles are relatively heavy, look up BrianTheBrain's designs; if your projectiles are fairly light, I would check out wyz2225's designs. A hammer valve seems like an obvious choice, but it would depend on the pressure you want to use, the intended projectile, the desired performance, and the desired function.
I would personally be more inclined to go with a storage tank (still hidden in the stock if you can achieve this) with a small chamber used for individual shots. Just use a 3-way valve to fill the chamber from the storage tank and pilot the valve (a QEV would do).
.though sadly i still cant get to lowes to get some materials.also i would have to wonder would it it be better to get a co2 tank and power it that way or would it better to do commpressed air.
