Your sump (continued). The refugium is just an open area of your sump where you can throw poorly behaved animals (a mean damsel, someone who was munching on your corals, etc) or a clean-up crew, or a breeding pair of clowns, or a big ball of rotating algae under a light to consume all of your nitrates. The latest trend is to put a purplish-red light on your sump so you can grow chaeto algae and then the algae won't be able to grow in your display tank because the chaeto eats all of the nutrients.
A lot of people take pride in their sumps. I have a friend who owns CNC equipment and built his own amazing acrylic super-sump with every custom compartment and feature he could dream up on his huge sump, which he keeps shiny and beautiful. Personally, I just went to the local farm supply store and bought an ugly 100 gallon rubbermaid stock tank, threw it in the basement directly under my 99 gallon living room display tank, and plumbed it up.
4. Learning your preferences. As you learn more in the hobby, you can answer questions for yourself, such as "Are you good with technology and computerized stuff?" If so, you may enjoy an Apex system to automate everything for you and monitor your system. Or, "Do you love tinkering with your tank every day?" If so, you may want to skip the Apex and do everything manually. Also, what corals do you enjoy viewing the most? I'd get to know some local reefers and check out their tanks, and ask them about their maintenance routines. YouTube videos can really be helpful too.