Oh!
Looking forward to them! (hi! :3)
Yay! The cover on the example is watercolour paper, but I forget what the gsm is, alas.
The securely unsecured format is a lot like one I learned that uses multiple tabs (through signatures) that lock in the same way (insert/bookmark) from a concertina inserted through a slit in the cover spine; the outside spine tab/flaps of the concertina strip could be left free, or folded and glued down. (and I was sure I had an example somewhere ... >.>;;))
Another interesting way, if you don't mind some texture (read: holes) in your cover stock, is to cut two flaps (one top, one bottom, each on one cover) running back to the spine ridge, and thread them through the slits in your booklet -- this one holds together pretty nicely for me!
It can save a bit of the cover sheet question, but does open up the "open tab space in cover" question. On the other hand, windows peeking into the insides have possibilities ~


Visually they what I put in the book, more or less; I can tweak selan.
Vaskr are noticeably taller than baseline humans, they have teeth like a carnivore's (including fangs) and they have horns that branch (you could give them antlers, it's basically the same thing, antlers just shed annually), this can give them a fiercer appearance.
Selan are more lean than baseline humans (more slender or wiry, however you like), and they have cloven hooves; this can be digitigrade legs as well, so something like looking like antelope- or deer- legs, with a long tail for balancing that has long silky hair, like a banner or pennant of a hair-tuft.
There's also ShoutingCrow's free to download and share etc Monthly Mega Dungeon Maker booklet ~ https://shoutingcrow.itch.io/monthly-mega-dungeon-maker