Many - if not the majority - of non-photosynthetic invertebrates are not good for beginners (sponges, NPS gorgonians, sea pens, crinoids, tunicates, etc.), if suited for a closed system at all.
Start with some easy fish and some soft corals until you are comfortable with running a closed system.
It's great that you are excited, and my compliments for asking questions before buying.
Cheers
Mike