jack rats take as long as any other animal to give birth, roughly a year. just wait.
no idea about your pathing/drinking issue, but I will add juice bar etc to the kobolds in a future update. Till then, please check the quickguide.png in the main folder for all available buildings they have.
bark scorpions should give life birth. RL scorpions do that too.
I'm used to seeing cats and moleweasels multiply from the first pair to at least half a dozen in the first year, and expected that if I started with 50... but I guess I should have given it more time before asking. I lost patience when my kobolds started starving. But I discovered that the starvation was related to the death by thirst issues, and had nothing to do with having no rats to butcher.
There was some kind of pathing issue on a ramp leading down from the 3rd to the 4th level of the cave. I set up a quantum stockpile to collect all my wagon goods on the 4th level and items were collected there, including all my newly butchered meats, prep'ed meals, and drinks. That ramp also leads to the tunnel I dug to the walled fish/drink area by the river and the aquifer drink zone. The ramp connection broke down for some reason, or worked unreliably from the start. Kobolds couldn't get food or reach the designated drink zone except those kobolds stuck inside. Military kobolds stationed there could not reach the location. I don't know why the pathing worked initially then broke down. There were no buildings blocking it or anything. I dug a channel beside the original down ramp and that worked for a while but broke down too. I then used tiletypes to put a wall over the original ramp and the level above it then dug a ramp there and it worked again. Anyway, probably an oddity with the map or a bug with the game, nothing to do with MW. I'll reload the initial save and see if it happens again just to be super sure it's not something I did.
In regards to the juice/tea, I guess that's just not implemented at all yet and kobolds just crave booze like dwarfs in the new MW version (so far). Is that correct? No ill effects from drinking alcohol? I've read and reread the old MW version's manual so many times that I was conditioned to think "stay away from alcohol!" with kobolds. I couldn't find the juice/tea reactions in the quickguide jpg or raws, but still thought I had to avoid alcohol. I guess I need to forget everything I know about MW(34.xx), and hope the update notes for MW(42.xx) remain accurate and complete.
Scorpions: really? Not like spiders and their egg sacs? Cool! But do they give birth in game with the current raws? Didn't see any child/birth related tokens there. Are MALE/FEMALE castes all that's required to breed? Guess I'll find out once I let it run a couple of years.