Fish, inverts, or Corals?
You can set it up easy if it is fish only. It is still pretty easy for inverts and fish. Corals require maintenance and might require immaculate water conditions starting with Hi-S/RO-DI water. Also your choice of synthetic or natural salt will matter.
If you want a mix of fish, inverts, and corals then you need to first assemble a list of possible candidates. Find their lighting, temperature, water current, and set up requirements. You also need to determine if your choice of fish/inverts are reef safe or if your choice of corals are fish/invert safe.
Once you have a list of the living stuff that you want and understand their care requirements you can then assemble the ecosystem to keep your tank running with minimal care and maximum health.