Yes, the Basic Sea Ranch with a 20-gallon hex tank would make a fine office aquarium and at 24 inches tall and has the height that is so important for a seahorse setup. But it is a bit under filtered and is best suited for one pair of medium Hippocampus erectus (Mustangs and Sunbursts) rather than two pairs. Keeping two pairs of seahorses in that particular set up would be stocking it to capacity, and would leave you very little margin for error. So I wouldn’t recommend keeping two pairs of seahorses in that system as a beginner, although it’s a great little tank if you’re willing to limit yourself to one pair of ponies.
One other thing to consider is that the 20-gallon hexagonal tank would be difficult to equip with a refugium because of its unusual shape. And I think it would be a good idea for you to have a refugium in your office tank for the "feed-and-forget" live shrimp you will be using to tide your seahorses over on the weekends.
For this reason, I’m thinking you may want to stick with a standard rectangular aquarium for your office tank, Lorli. Either a 20 gallon Extra-High All-Glass Aquarium (20"L x 10"W x 24"H), or better yet, the 30 gallon Extra-High All-Glass Aquarium (24"L x 12"W x 24"H), might work well for you. Any local fish store can special order one for you and they are economical tanks that also have excellent height for seahorses at 24-inches tall. The 30-gallon version would have a footprint of just 24" x 12" — not much larger than the footprint for the 20-gallon hex tank — so it could also serve as a desktop tank. And, most importantly, it has the right dimensions to accommodate either a hang-on-the-back refugium or even an in-tank refugium for your live feeder shrimp. With the right filtration system, this tank could easily support several large seahorses.
Let me know if that’s something you are willing to consider and I’ll be happy to discuss how to filter and set up such a tank to create an ideal environment for Mustangs or Sunbursts, Lorli!