I made my vx pack out of vx21 bottom/back (back as in strap points), vx07 sides/front, but because as noted, vx07 is pretty thin, it's really just 1.9 oz nylon with extra backing and an x grid, I used 200d for pockets, so the actual contact area of the pack bottom is vx21 and the lower sides is 200d over vx07, and since I don't really care if the pockets get small holes, that's fine I think. I wouldn't use vx07 if there were no pockets covering it on the lower sides, I don't think it would last long unless you only walk on broad 'wilderness highway' type trails.
If you're bushwhacking a lot particularly through chaparral type pointy sharp stuff, use the heaviest you can manage.
Since my top doesn't really touch anything I used regular but heavy coated 1.9oz nylon ripstop.
Side pockets are hard if you make them actually shaped, I did a lot of model prototypes using socket wrench long sockets to model the water bottle weight, took a lot of revisions, but once you get the pattern they are not that hard to make. I rejected any type of mesh for side pockets due to stretch and holes grabbing branch issue, so that turned out nicely.
Working with vx material is extremely pleasant by the way.
I used 200d / 3d mesh for straps.
+1 on diygearsupply, that guy works hard at getting deals and offering a wide range of useful fabrics, particularly worth noting is his excellent selection of good quality gutermann threads, I suggest buying one of each he sells because they are very cheap and worth stocking up on and since you are already paying shipping, just toss them onto the order.