Hey Maggie,
1)Crystalwort is like a small/skinny version of liverwort. Both of them have dichotomous branching (they split into 'Y' shapes). Its more of a lime green color compared to Liverworts deep green.
2) You can probably track some down at a local fish store. Its the new fish craze to string it submersed to rocks or wood to give an underwater moss effect. Normally it will be found floating at the surface of water like Duckweed. And if all else fails do a google seach for "Riccia Fluitans" and go from there
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3) As far as conditions it needs to be constantly moist (in my limited experience). I currently have some growing in completely sealed dart tanks on some spagnum, also some in water features that my darts trampled into the gravel, even on some moist wood. In the few tanks that have it my light ranges from 3000k-5000k (the 3000k is very reddish so thats a guestimate on the color scale as ive thrown out its box, but it seems to do better in the 5000k range).
Lastly IMO its a nice change from moss but im not sure if it compares much visually to liverwort. I have however seen some sp. of Riccia that look exactly like mini Liverwort but ive never been able to track them down, so your best shot at getting some seems to be Riccia Fluitans. Good luck.
-Martin