well i have a 14 biocube so i can help out a bit with it, mines been up for about 8 months or so.
for a CUC you could add more blue legs and snails to keep algae down, addition of rock is okay as long as its cured or you might have another mini cycle.
yeah pajama and bangaii cardinals are okay for the tank size though they prefer groups so idk how they'd do in a 14G alone. most watchmans are good for nano tanks.
the cave goby (if i'm looking at the right one on liveaquaria.com) is good, but they jawfish needs a deeper sandbed and they are notorious jumpers, i see one in my LFS
constantly trying to leap out of its tank (so much so they put a piece of plastic on top with a rock to keep it in the tank)
oscellaris and percula clowns are good for nanos as well, i had a pair and they were great!
you could do a clown, watchman, and maybe a peppermint or cleaner shrimp too, just look around liveaquaria.com for fish and look at the tank size requirements and needs etc. about 3 fish/larger inverts are what you can keep
i have a firefish goby(Saltwater Aquarium Fish for Marine Aquariums: Firefish
) and a starry blenny(Saltwater Aquarium Fish for Marine Aquariums: Starry Blenny
) in mine
as for corals with the stock lighting i'm assuming you have you'll have to stick to mostly softies like mushrooms, zoanthids, polyps, ricordeas, and xenia.
right now i only have some pompom xenia and two different color mushrooms, just read the requirements as well on liveaquaria, low to medium light is jsut about all you can keep (medium light being corals you can only keep at the top of the tank really)
green star polyps, tons of colors of zoas, tons of colors of mushrooms and ricordeas, all good for a biocube reef
hope i helped, and good luck! my biocube has been a ton of fun for me, dont listen when people say nanos arent for beginners! they just take more work!