[Qlong]

A note on a few of the items you suggested for your WE.

Selector switch, no mods but most are semi auto only, if you use one, your WE will be limited to that only. You can purchase an auto/semi safety but you will need to modify your sear and auto sear.

Mag release, because the top of the WE mags are flat and not contoured like a real magazine, you will have to press the mag release to insert a magazine. Otherwise you need to grind or machine down some material off the mag release.

Upper Receiver, mechbox needs to be machined down, hop-up chamber 3 and 9 O'clock tabs needs to be shaved off.

Charging Handle, Eh, depends on brand, USGI/standard charging handles will probably need to have a pin inserted into it to properly grab the bolt carrier. I would pin the bolt carrier, a cheaper part. Ultor/BCM grabs the bolt with no problems.

Bolt catch, completely different design.