Love the tank size and how low it sits, pretty sweet.
I'd suggest rather than upgrading the skimmer now is just running it for a while and adding a second one later. Why not run two small skimmers instead of one large? Actually makes more sense in a lot of ways when you think about it. Looks like you'll need a bigger sump to fit two but I'm pretty sure you probably need a bigger sump anyway
. If you loose just an inch off the main display that's 21+ gallons alone plus the extra volume from plumbing, skimmer and the other tank you're setting up. Doesn't quite add up properly in my head so be careful of that, might need check valves as a minimum.