I can't offer good advice, but I can share my experience at least. I think different dart species vary. I have a dendrobates tinctorius 'cobalt'. I wouldn't say he jumps around a lot, but he does like to occasionally climb the background a little or climb up onto my broms. I actually have no idea how he gets up there, because it usually happens when I am sleeping and I find him there in the mornings. He mostly likes to roam around on the ground. I don't have springtails in there yet, so can't help you there. I imagine, though, that he would catch them if they came around the top, as opposed to digging around for them.

I also am not the one to give advice on tank size... so stay tuned for the experts on that one. I have a 12x12x18 (which I know is too small, but that's a long story). It has a good amount of vertical space, and I was able to sort of build upwards from the front to the back with substrate and then angle logs/plants/branches to give more space to climb around on. I also just really like the visual appeal of a taller tank though.

Oh, and I do have a water dish, and he does get into it at least once a day typically. I like the idea of things like those monkey pots or whatever they are called or upside down coconut halves with puddles in them for a more natural look though.