Welcome to Reef2Reef, and to the hobby!
To start, I would get a tank of at least 30 gallons, preferably 50, just because it's big enough to stay stable for corals if you ever decide to keep them, but water changes won't be expensive. With your background in planted tanks and shrimp, it could be cool to see you try a macroalgae display tank, essentially a freshwater planted tank. But keep in mind, many corals can be compared to plants in one way or another, as several are indestructible and several others are less so.
I cant wait to see your progress, keep us posted! Good luck and God bless you!