if it were me... 300 gallon salt tank... 75 gallon sump filled with live rock and sand large skimmer... and the ocean clear on return end with chemipure... simmilar to my old set up and a friends now set up for sharks..
Also do a "search" on MFK via the "search forums" box screen left for some of the questions (topics) you have as many of them have been answered and thoroughly discussed. I know sometimes its quicker to just ask a question; But, it may be more insightful to read other threads that pertain to the questions you have as you may find some well-developed responses that satisfies some, most, or all of your inquiries.
what is the smallest species of freshwater rays that can be kept in tanks? i'm asking out of curiosity (i'm sure my 30g is way too small for any ray) but if i ever set up a new tank, i want rays