Some words about the Lumber Mill.
Build it. Asap. Don´t delay it. It´s a cash cow. Ok, not Workshop level cash cow, but still the second best.
In previous versions it was not so clear, because the slaves were tied to the Mill, and slave work it´s a scarce commodity, and you will need slaves for Zapin fields, for the gold mine, for the rebellion and, if you are Aesir, for your church. But now that you can shift them to some degree, it´s a no brainer.
The investment it´s modest. 30.000 as a starting point it´s not a lot of money. Upgrading your workshops will cost you 10.000$-10.000$-25.000$-75.000$-200.000$. Upgrading your workshops (two) should be your economic priority, but you can argue that before the 200.000$ upgrade, or even before tackling the 75.000 upgrade you must invest in the Lumber Mill. In my current run I have opted for a middle ground. I have buy the lumber mill with one workshop upgraded to the 75.000$ point, put my very best workers on it and keep the other with a worst crew just at 25.000 for the moment.
You will need some guards. Half a dozen do the trick. Most probably at this point you would not have finished yet Ford Serra Quest, so you must send some of the girls you have captured from the band of Stoke Hills, or the random bandits. If hardly pressed, you can even send some low tier mercenaries that you don´t care about.
First thing first you must pay at least two upgrades to the living quarters, in order to prevent desertions. That´s another 24.000$. And the start pouring slaves not stop. Don´t rush to enhance the fields. Depending of how many slaves you have working the price of enhancing the fields varies. I´m not sure of what are the jumping numbers, with with very few slaves the first upgrade cost it´s 4.500$, with 20 (may be a bit early) goes down to 2250 and then, roughly at 40 slaves, down again to 1125$. At this point, upgrading the tree fields tree times will cost you roughly 30.000$
All in all the total cost of a state of the art Lumber Mill it´s, give or take, 30.000 ( Buying it) + 25.000 (upgrading the living quarters) + 30.000 (upgrading the fields) + 75.000 (75 slaves, you can send there the crappiest ones) for a total of 160.000$, and you must have upfront only 45.000 (buying the fields and upgrading the living quarters), the rest can be paid at your best pace.
And what you get from this? Well, roughly 4500 of timber per day. You can either sell the timber at 1$ apiece or use it for your own workshops (this timber would be valued at 3$). I advice not selling the timber at the start, but build a reserve of timber. Because latter on the game you will get the gold mine and the steel mine and you can transfer the Mill workers to them. When I have buy the gold mine I let the mill empty and have send all the workers to the gold mine, and I get 1.000.000 per week (until depleted), and later on the same will be done with the Steel Mine (less profitable but hey, it´s free!!)
Let´s compare then the Mill with the Walton Armory investment. 160.000$ for the Mill, 200.000 for Walton. Walton Armory yields 1.100 plus 650$+/- from the accountant & Mc admin (my admin it´s high at 86), + 350 From Becca or roughly 2.100$ per day. Roo Shop it´s 75000 (so half Mill ) and you get all in all 1000$. The lumber mill it´s twice as profitable as Walton Armory or Roo Shop (or more)