Take workers, get a worker human slave. Now you have a slave who starts with 20phys (worker class+outfit) who can have 220% efficiency while collecting wood (50 from worker, 50 from stuff they gave you, 10 from being a slave, 10 from being human), take watchdog later for another 10 phys
Sell the wood when you need money, and later buy her a Pickaxe when you want to farm mythril --> 75/unit @_@
2 watchdogs slaves can boost their obedience themselves and will make you TONS of cash
I find Servants a bit weaker but they help with obedience