The Gathering Wilderness
Your characters are all masters of a guild in the kingdom of Taol-Kaer, residing in the capital of Osta-Baille, where you've lived for most, if not all, of your life. Your characters are all well-known, whether it be by reputation in the case of thieves or assassins or in person for more 'legitimate' activities. You're free to come up with a backstory for both yourself and the guild you run, but they should all make sense within the context of the kingdom you're in (I'll upload a book with background stuff this evening). For the sake of plot, you're not allowed to be antagonistic toward Taol-Kaer – everyone should have a vested interest in its success.
Your guilds work primarily by contract; people or organisations who require your services will petition you to complete tasks, the guild will send a qualified person and will be paid for completion of the task. As leaders of the guild you tend to stay out of the more day-to-day tasks, but will venture forth for particularly difficult or important assignments.
All of the 5th edition classes listed on this page are acceptable except for Warlocks: https://www.dandwiki.com/wiki/5e_SRD:Classes. I can explain how your class would fit into the lore if it isn't obvious.
Everyone starts with 500gp + d10*25gp and can also select one magic item to start with – this item is something you acquired in the past and that you used to help you form your guild – it should make sense in that context.