I think maybe 3d6 could work. I'm more than willing to work on preliminary numbers.
Also I think maybe something more fluid could work as regards background and/or perks/traits. Defining a set is all fine but allowing other players to suggest and create is best for everyone imho. Just requires the player to accept the GM's decision and the GM to willingly test out the numbers and fairness of a proposal.
When the guild is more functional I'd certainly be interested in hashing ideas out in more depth.