Playing on more than one server
You can only have Toons on one server. Once your character slots are full, your options are to Buy more character slots in the gem store, or purchase a second copy of the game.
(Actually, buying extra copies was a thing a lot of people did in GW1 for more character space, but shhhhhhhhh…)
You can’t have characters on multiple serves.
You can be in a guild cross-server. although you won’t have use of any of the upgrades (i.e. bank, bonuses, etc) because the guild rank is different depending on the server. But you can still chat.
Unfortunately, No, even freeing up a character slot will not let you create a new character on a different server other than your home server. The reason is to prevent abuse in world vs world (also the reason why server transfers were extended to once every 7 days from once every 24 hours).
Fortunately for you, you’re not forced to leave a guild on a server transfer, you’ll stay in the guild but you won’t have access to all the unlocked that are tied to your guilds primary server. You’ll have the ability to communicate with guild members on different servers though. You can however join a guild on the new server (it will take up a second of the 4 account guild slots).
Ferguson’s Crossing
They’ve implemented the Guesting feature, I am told. You don’t have to transfer to play with your friends, just Guest over to their server. There are some limitations on using this feature.