Way too much stuff to explain in detail, but I'll try and get you started on some things...

First of all I have no idea what "armor mitigation" is, so I'd venture a guess that we don't have that in UO

As for stats, here's what they do in a nutshell:

Strength: determines your total hit points and the total weight you can carry. Also adds a slight damage bonus if over 100.
Dexterity: determines the amount of stamina you have, which in turn determines the speed at which you swing a weapon. Also used for other speed-type checks for other skills, for instance, more dex makes your bandages apply faster.
Intelligence: determines your total amount of mana, affects mana regeneration rate.

As for the skills you mentioned:

Swords: affects your hit/miss ratio and your defense. Basically determines how often you hit your enemy and how often you get hit.
Anatomy: gives a damage bonus and improves the amount of damage you heal with bandages. Also enables you to cure poison and resurrect others through the healing skill, if both are high enough.
Lumber: slight damage bonus when using axe weapons, lets you chop trees for wood!
Healing: lets you use bandages to heal damage. If high enough and coupled with anatomy, you can cure poison and resurrect players using bandages too.

- you can gain stat points when you gain in a skill, I think the intervals for stat point gains are 15 minutes. As in, you gain in swords and get +1 strength, then you can't gain a stat for another 15 minutes. By locking different stats in the status bar you can choose which stats go up, which go down, and which stay as they are.

- using a shield depends on your own preference and the skills you have. If you use bushido, don't use a shield. If you don't have parry skill, the shield is only good for the few extra properties on it but won't actually block much anything.

Someone else can maybe take over and go into more in-depth warrior template stuff as I'm hardly one to work on most efficient characters... too much roleplayer in me for that...