So the general system will be 100 stamina/action points, give or take some bonuses. Let's say a realistic cap is 200 stamina and that's with a lot of questing, PK rewards, remorts, etc.
From there, there's a regen rate of between 2 and 10 stamina per second depending on the bonuses and the focus you've taken. I imagine with remorts and PK rewards you can opt to choose between faster stamina regen, or more stamina points. Faster regen is great for more consistent speed, but having 200 stamina means you can get off 4 rounds of something in rapid succession that before you'd have been lucky to get 2.
In terms of stamina cost, I'm currently going with a relatively simple system which I think we're going to want to keep. The formula is as simple as skill level * skill tier / 4 + 1. So a level 50 tier 4 skill is 50 stamina. A level 8 tier 1 spell is 2 stamina. We may need to adjust this a little, but I think generally speak it makes sense for the stamina formula to be skill level and skill tier based and then for skills/spells where the stamina cost is lesser or greater than the value of the skill/spell in all honesty we probably have the wrong tier/level to it.
For this particular system I've drawn out a scenario below:
Once begins a fight with the Minotaur. [100 Stamina]
Once cleaves the Minotaur. [-12 S] [88 Stamina]
Once turns active dodging on. [-8 S] [80 Stamina]
Once dodges the Minotaur's pierce. [-2 S] [78 Stamina]
Once cleaves the Minotaur. [-12 S] [66 Stamina]
As I look at the example I start to see that maybe our current formula is a little weak at a 100 stamina base. I'll probably revise that. I also start to see that there's a lack of skills that currently could take advantage of stamina. This could be where new skills and some of the "reshuffling" come in to play.
I think one usage of stamina could also be for maintaining "passive" skills and deciding which ones are on and off. The choice between going full evasive or just taking the damage should depend on the situation. Evasion or shield blocking takes up some amount of effort. I can see the same concept being applied to certain spells (although not all).
Anyway, that's the brain dump on this so far. I think a better formula currently may be skill level * skill tier / 2 + 1
In that situation we'd have Cleave costing 24 stamina per usage or basically 4 cleaves in a row followed by some time to regen. That seems a little bit more logical given that when I first wrote the formula I was assuming we had some tier 4 level 50 master skills that people were using. We should also be thinking about master skills like that that we can bring in.