1 - implement actual guild hall, with a button to teleport there, or implement a button in guild tab where officers and leaders could set some one's residence as guild hall.
2 - A good addition would be, allowing people to buy 2 NPCs for their guild hall/residence (must be in guild and as per suggestion above, should be as as guild hall). those both NPCs are "guest" guild traders of allied/friendly guilds.
3 the banker NPC you set in your residence, should give access to you own guild's bank and store.