a little late on the scene but here I is!!
sexy shrimp are by far the coolest little shrimp. I bought four of them for the first time about 4 months ago and put them in my 7.5 tank. I purchased mine from
www.liveaquaria.com and with shipping they ended up being close to $20 each, but they aren't sold locally so I really had no choice. the size when they arrived was about 1/4"...very tiny. they've grown to about 1/2" or so now.
typical behavior of my four is they have one particular area in the 7.5 that they stay in, on the left hand side of the tank on one specific piece of LR and the small area of sand bed in front. they never stray from this area. they generally stay together as a group but occasionally they will pair up and wander to different parts of the rock. they do need to be kept in groups of three or more. In a 10 gal tank you could easily keep 6 or 8 of them since they stay so small.
I'm setting up a 2.5 gallon specifically for mine because when I transfer the contents of my 2 nanos into the 30 cube I just bought I'd rather not make $80 worth of shrimp a quick snack for my six line wrasse.