There are many ways to have a successful reef aquarium. Here is my opinion on the things you mentioned above:

The Eheim canister filter is not needed and would probably become a nitrate factory for your tank due to catching detritus that will break down into ammonia.

A protein skimmer is not required. IMO small skimmers are junk anyways (although it should be noted I haven't tried one in quite a while maybe someone has finally made a good one). If you keep your fish stocking levels to 3-4 small fish that don't require constant feedings, you'll be fine without one. Also the type of corals you want to keep plays into this as well. Zoas will do fine with no skimmer. Acros would be a lot more difficult. I have no skimmer on my 30 gallon tank and have 4 fish with a tank full of soft corals.

A sump is not needed. I like the back sump area of the all in one tanks (when designed correctly). They hide the equipment without having to have a separate tank. But you can accomplish similar things in a large hang on the back filter or refugium which has been modified to work like a sump. One of the most important things you need is to break up the water surface to get the "film" that will float there from animal waste. Typically this is done with a surface wier on the intake into a sump...but again, can be accomplished with modified hang on the back filters or a back chamber area. Given the that your tank is only 12-inches front to back, I doubt you want to occupy that much space for a back chamber/sump area. If the hang on the back options don't thrill you, then you may want to consider a sump.

You don't need UV. UV can be handy to prevent disease in fish and keep the water crystal clear. However, there are those that feel it robs corals of food that should be available in the water column.

I would say 4x is on the low end of for flow. That would be okay for flow through a sump, but your over all flow should be higher than that. In addition to a Sicce 0.5 pump (185 gph through my back sump area), I also have a Vortech MP10 running on my 30 gallon. Granted the MP10 is dialed back most of the time.