silver dollars like to school so get atleast 3, but they look great if you have 4 or more. i have 4 and they grew like weeds to the 3-4" range but now are growing much slower.
most likely the lfs will sell you redhooks as silver dollars but if you do get true silvers you can keep them in a 55 for life probally but i have heard of 12" silvers so beware