It is possible to get a cape in Pre-Searing, it costs 2,000 gold. To get a Guild Hall, however, you must reach Lion's Arch in
Post-Searing, which is roughly 1/3 of the way through the game. You talk to the NPC on the boat there, and check out the different halls. You will have to purchase a Sigil, which runs for around 20,000-25,000 gold. Then you take the Sigil to your desired island, and say "Yes" when the NPC asks you if you want that island as your Hall. Note, you have to have a cape before purchasing a Hall. Hope this clarifies things, feel free to ask any further questions.
Edit: When looking for a sigil, try posting "WTB Sigil" around Lion's Arch, and hopefully you can find one for about 15,000 gold.