After reading over your thread and what you want, I'm thinking that you are closer to having a DIY system fit your needs, and may be disappointed with the RSM250.
You said you wanted LED lights and are only partially interested in the DIY/tinkerer aspects. This is a big expensive project on the RSM250, and reading this forum, I'm not sure anyone has cracked the code yet on a successful trouble free installation with a true 3W set up that are recommended for reefs. LED in a closed hood is a challenge.
You want the bigger fish like Tangs. Any 65 gallon is too small for fish like that. For the RSM250, review fishes (adult sizes) of 3" - 4" maximum, with maybe a few larger carefully chosen fish. There are lots of great choices in Basslets, Cardinals, Blennies, Gobies etc. Your thread didn't mention the desire for corals. If it's a fish-only tank you want, you can engineer them to be much simpler and less costly. It sounds like you want big active fish and that dictates a large DIY system or one of the new Red Sea set ups.
Did you say you were going to put it where your biocube is now in your pic (nice tank BTW!)? That location looks cramped I think. You want a few feet on each side ideally, and some room to work on the back (6"-8") to plumb chillers, add fluidized reactors if you need them, etc.
Sumps. Personally, I tried to avoid a sump & that made the RSM250 especially attractive, and I've never looked back. If you have your heart set on a sump, other DIY options or an AIO unit w/ sump might be the best option. it can be added to the RSM250 but you need an overflow box and your product choices are somewhat limited in this area.
The RSM250 is easy to set up, own and operate in the long term at a reasonable price & one company to go to if things go wrong. For example the hood design is a a great design IMO, making all chores easy, and that's hard to get in a DIY system since it must appeal to a wide variety of buyers. I'm a motorcyclist. Some friends & associates HAVE to build a custom bike with every detail to their specs. Others are happy with a factory configuration with just an accessory here and there. Different strokes for different folks.
The RSM 250 is a great system. It can accomplish anything any other 65 gallon system in keeping appropriately sized animals. Good luck whichever way you go.