Estates are based on acreage and determine how much you can build. The large your estate the more you can build. When you join Eqcetera you have 10 acres of land from there you can upgrade up to 500 acres! Non upgraded players can only upgrade to 25 acres.
Barns increase horse space at your estate. The more space you have the more horses you can own or the more horses you can board!
Training facilities are needed to train your horse in their disciplines. Training facilities can only be bought by upgraded players.
Show arenas are needed to show your horse or host shows. Show arenas can only be bought by upgraded players.
Feed storage is needed to keep feed. All horses need 1 feed a day.