I would recommend having 1 character be the maximum in all 7 crafts, at a minimum. It will save you time in collecting motifs in order to make gear.
Perhaps, most importantly, a lot of furnishing plans are "multicraft" skill needed... it's easier to have one character with all the skills, to make this as painless as possible
There are enough skill points in the game so that you can be maxed out in every craft, AND still have your character able to do PVE and PVP content.
Every character should have maxed, or near maxed Alchemy and Provisioning. At least enough levels to unlock the Passives that increase Durations. Thankfully, those skills level really fast.
As for Writs, only max level Writs give Master Writs. But you need to invest around 50 to 60 skill points to do Max Tier Writs. Me, most of my characters do L1 Writs, as the Gold and Material Rewards are the same.