That is a very nice looking setup on D Colony.
However I personally like keeping the nests and outworlds as separate structures connected by tubing.
An all in one like that would mean anytime you need to clean the outworld up, it will be full of ants and you'll greatly disturb the nests in the process as well.
With separate nests and outworlds you can easily plug the nest/outworld port, remove any ants in the outworld to a temporary holder. Clean up the outworld, dump the temporarily held ants back in, and open up the nest access again. And doing so will generally not disturb the nests, keeping colony stress down.
Just say'n in terms of longer term upkeep effort, separate nests and outworlds will be less work to maintain than an all in one.
I've not made any full formicarium or outworld, i've only made nests so far.
I'd say be ready to make 2-4 nests before you get one you will want to use. It's just a fiddily fine details matter(tiny holes can leak/not perfectly level/watertowers float/sand shifts around/etc. etc). It is the kind of thing i'd say no one willl ever do right on their first try. So be ready to pour a few failures as you go.
I've got 3 good nests in use so far(and about to make another one). But i've poured 7 in total, with 4 of those going direct to the trash.
I'd say no sand mixed in the grout. Though i've not tested with sand, all my own nests have been good with no sand mixed into the ultracast.