Sounds like you are already in the game. If your looking for all in one with refugium capabilities, basically add salt water, the Biocube 29 is a great option.
If you plan on plumbing it together to your main display tank I would buy just a 30g glass tank and call it a day. You dont want to spend $250 on a Biocube if your going to drill on it. Spend less than 100 and buy a simple glass tank. Best of luck to you!