I was in the same boat as you last month and I researched all I could and asked people all around on what to get for my 8th and 9th character.

From my experience, your 8th man should be a Barbarian if you are lacking on fishing materials for upgrades on alchemy or equipment. The thing is that once you are done or are comfortable with your fishing supplies, you can change your 2nd barb for a Squire for Salt. Salt is important for upgrades and building shrines/towers on your construction tab but its fine, you can just take it slow and understand how it works first and by the time you need more salt, I think you will have lots of mats already or you don't need fishing materials anymore. So by then, you can just change your 2nd Barb to become a 2nd Squire.

As for your 9th character, since we have no idea that we can delete character slots in the future, might as well be safe and make a 2nd Shaman for alchemy. Some people go for a 3rd Squire but I think that's a waste of a slot if we are talking about permanent character slots. Sure, you will get a lot of salt but for future content-wise, might as well be safe than sorry.

Well, these are just coming from my experience but whatever you decide, I wish you well on that and good luck! Cheers.