Hi Andy,
First off, great choice on the new armour. One of the best out there as its a direct cast off of the original - awesome.
Personally I'd say you're done with the weathering at this stage.
As for the backpack weathering, go steady. Although weathering of any TD parts is personal we want to avoid going too heavy with it (as well as not enough). The good thing about the backpacks is that you don't have to apply much to be accurate. Again, I'd say that you're there with the amount you've already done.
The only thing I'd suggest you need to do at this stage is tone down the "tea stain" on your pauldron. Despite the name we give this, it's actually meant to replicate the sticker residue from where production crew removed a circular sticker from the motocross chest pad (pauldron) prior to filming. Due to the sandy/dusty environment in Tunisia, dirt got stuck in the residue and left the "tea stain"
A lot of people make this mistake and try to over compensate for how it appears on screen.
I'll get back to you with an approximate size of the lab pipe as I have one in my garage at home and I'm still at work at the moment, unless someone can answer in the mean time.
Looking forward to seeing your bee stinger on the pack. Just remember the metal brackets go on the outside of the container however wrong it feels!