It all depends on what parts you pick honestly, and depends on what how LW you want it to be. Personally i would use a regular forged upper, and would not think of using a SS barrel. I am not trying to put your build down or put you on the spot at all so I hope you didnt think i was calling you out.
The Vtac handguards are light for sure, i just got a set in and think its a very well made peice of gear. I also like the apex, and have been looking for an excuse to put a set on some build, but i cant figure out what yet. There are some doing LW builds that are aiming for the LIGHTEST weight they can get, and the only handguard that will work for them is a custom carbon freefloat tube. These are the same guys that will find a slick side forge upper and possibly even mill it more, and only use a pencil barrel. So i mean there are different levels of LW builds, and you need to figure out how light you want to go, and also what use the gun will be seeing.
Some people say that pencil barrels are not the best for live fire course where alot of rounds are sent down range quickly because the barrel heats up fast.
If you let us know to what point you want to take the LW aspect we can certianly guide you in which way to go. I suspect for what you are after a nice non ss barrel with a good medium or light weight contour will be great, along with the Vtac tube will be great.
Pat