This is my first time posting after lurking and learning for over a year. I have built 3 AR's, all with 16" barrels and carbine length gas systems. Now I am in the process of building my 4th but this one will be using an 18" or 20" barrel chambered in .223 Wylde having a rifle length gas system. I am looking for info on what type of buffer/tube/spring will be needed for proper BCG operation. Any tips and suggestions would be greatly appreciated.

Nobody can really answer that for you. It depends on what size the manufacturer drilled the gas port on your particular barrel. Most likely it will function fine with a standard carbine buffer and spring (you are going with a car stock, right?), From there you can try heavier buffer or extra power spring to tune it and get less recoil if you feel the need.

Ive got the silicon heavy duty spring and carbine buffer on my 20" wylde from Green Mountain. Carbine spring would work just as well.

bro:  I recommend you go with a GI rifle length receiver extension, a GI rifle buffer and an aftermarket rifle spring (e.g., JP Rifles) for the ultimate in reliability and durability.  Carbine buttstocks are a compromise that is out of place on a heavier rifle, IMO.  My latest build has a heavy 22" Wylde barrel (1in8 twist) from Compass Lake.  With my selected handloads, its routinely printing 1/2" groups at 100 yards from a rest. - CW