I took a look in my garage and realized I have enough spare stuff in there to run a fully independent tank so that's what I plan to do. I just need to build a stand a find a good sized sump which I may just go with a Rubbermaid tub.
It'll have an Apex running everything with a CaRX, skimmer, biopellet reactor, and a GFO reactor. I'm basically mirroring my DT, right down to the lights as I want them to have minimal stress when moving to DT. Also, I plan to have it setup right so I don't have to do water changes as well with this tank. Just replace media when needed and test every quarter, except for alk that is, that's at least a weekly task.
It's both amazing and sad that I had enough spare parts to build a mini-me tank.