I have a similar shelving unit from lowes: 1000527
You can fit 3 10's on there long side to long side, with some overlapping of the shelf. I cut a piece of plywood that hangs over front and back. along w/ a 20g long supported by dimensional lumber.
you can't trust the actual shelves for one second. that pressed wood crap, though rated high, probably can't withstand the weight per sq/inch that our tanks are.
Honestly, I don't trust the shelf with my tanks on it, but it's all I've got right now. I'm already noticing some stress on the shelf mounting points; mine uses the same sort of mounts as the one you're looking at, just not hidden. I also feel like there is some bowing in the metal, but my level says otherwise... something just looks off about it.
I intend on building something out of 2x material once the weather warms up as I really don't trust this thing. It has zero racking strength (side to side) and if pushed hard enough from the side will most likely crumble to the ground.
I have mine in 2 parts, which the one you're looking at can do. I didn't need the height, so have one for a basic work top/storage, and one for the few tanks i have on it.
I don't recommend it... especially not with the amount of tanks you're looking to put on it. the shelf is a cheap piece of garbage.
I had a buddy using one at work for as a server rack (computers) and they replaced them for failing.
it seems like a great cheap solution... but cheap could cost you 16 tanks and a ton of clean up.
here is my pre-water