Main chars:
I thought about skills trees right now it is a little mess, but if we get simple skill trees for different "jobs/profesions" it can be used to boost character level up.
Something like personal belives in hnh you have few levels, you can switch it after some time...
idea is simple create char, pick skill tree for example "Farmer lvl1" then all skills requested to make a farm (agri, cotton and cabbage planting, botany, hori etc etc) will require 10% less profs, if you go further and pick "farmer lvl2" it can lower skill cost by 20%, of course to switch from level 1 to 2 you must wait few hours and if you would want to pick different tree you have to decrease farmer level one by one to 0 (or maybe to some low value*).
At some level it could boost farming, so if you are one week (more time = higher level) farmer you could get faster or more crops than first level farmer.
*To make game playable we would need few low level profesions per single char, so maybe it could work with cap max 10 "jobs/profesions points" and we would be able to split them on jobs we need on our character. If max job level would be 5 then single character would be best only in two different jobs (like farmer and forester for example, or hunter and fisherman, or miner and blacksmith etc etc I picked those that are somekind related, but it wouldn't be rule).
Of course proficiencies level would matter all the time or even better higher proficiencies you get more "job points" you can assign
Job level would be to boost it a bit at start, so groups that would split their roles would get everything faster and cheaper.