You're welcome! :) The Magic Realm is actually more like four lots. The Magic Headquarters where the Sages live is the main one where anyone that goes to the Magic Realm will materialize after going through the portal. It is possible to bulldoze and build on that lot, but your Sims can't live there, it's more like a venue/school for Spellcasters to learn magic from the Sages, practice magic, duel, use the caldrons, find tomes, familiars, etc. Not really relevant since you're not planning on going there anyway but thought I'd let you know what's in the Realm.
There is also a 'town' area called Casters Alley with shops for Spellcasters to buy magic related things; tomes, brooms, wands, potion ingredients, familiars, etc. Another lot is the Dueling grounds for Spellcasters and the last lot is an area with an inaccessible abandoned greenhouse, a fishing spot and harvestables needed to make potions. Each one of these are not buildable. All four of these areas are on separate floating 'islands' only accessible by the magic portals or if your Sim is a Spellcasters they can fly there on a broom or transportalate. They can't go anywhere in the Magic Realm from Glimmerbrook though except to HQ, then they can go to the other places. That's it.
Have fun in Glimmerbrook, it's a beautiful neighborhood, I love it! <3