one on its own is fine, but if you do get two, make sure you dont get 2 males. I had 2 males in a 20 gallon and they squabbled a lot. One made about 3/4 of the tank his territory and the other just hid in the back corner behind the
driftwood.
Ive had 2 females together with no males, and they were fine together, no fighting.
as far as difficulty to keep... they are fairly easy to keep, you just need to keep up on water changes. instead of doing a 25%
water change every week, do 10-15% twice a week.