I basically agree with all comments above. Some additional comments:
Can't believe I bought the game but never played it at launch. It's pretty damn good. Some quick questions:
1) Should you use the tactic mode or just control your character and let your companions do w/e they want? What do most people do? When ever I click on them during a battle, well they have all their spells used up anyways. Plus sometimes the camera angles get weird. Yet, I don't know how good the AI really is.
I use Pause way more than I use Tactical. Like to make sure everyone has Barrier or Guard (Taunt), or drinks a Regen potion, etc. Then let the AI go while I focus on my IQ.
That said, I've been experimenting with "disabling" Pause and it's like playing a completely different game. More action/shooter than RPG.
AI is really bad at DW rogues and Reaver Warriors. Other Warriors it does okay. Archers it does well except for Leaping Shot (near a cliff, etc.) Mages it does very well, sometimes better than me! Like I might not notice a party member is down, but the AI will whip up a revive almost immediately.
The reason your characters always have no mana/stamina left is because you haven't reserved any. That's actually a good thing, you don't want to handicap the AI by starving it from resources.
If there is an ability you don't want the AI to use, but you do want to use when you control the character, make sure it is an active (takes a slot from the 8 active) and is Disabled in the AI settings. For example, I like to use Grappling Hook when I control Cass or Blackwall, but I hate it when they steal a kill by pulling it away from my killing blow. So I disable it, but leave it active.
2) I am not big into lore or anything, but DAI lore is pretty interesting. I made a character who is supposed to be not such a good person. Not EVIL, but you know someone who doesn't give a ****. So every time I make a decision or respond to someone I always pick the idgaf answer. Like when people are like OMG IS IT TRUE YOU ARE THE HERALD OF ANDRASTE??? I just say I DONT BELIEVE IN YOUR GODS, or something like that. But recently I started to notice that my companions approve or not approve what I say. And, I didn't know that. Specifically Cassandra always disapproves. Does that make a difference? Should I try to gain everyone's approval?
Just go with it. My second run was a Jerkquisitor and it's fun. Who cares if some party members you never take with you end up leaving? Just be careful with the ones you care about. You always have one shot to improve their approval before they leave for good. So you'll get some warning. Save their personal quests for that emergency and you should be fine.
Solas won't leave due to disapproval, so feel free to insult him as much as you want.
3) Best armor/wep in game dropped out in the world or have to be crafted? And I noticed not all vendors carry the same loot, so I am thinking as you get to new areas new vendors unlock new and better stuff?
In general, you can craft better weapons than you can find, and crafted weapons don't have level restrictions the same way looted weapons do. So yeah, crafting wins most of the time. There are some exceptions, some looted weapons worth adventuring for, particularly at low level, but yeah.
New merchants do unlock new stuff, but not necessarily better.

There are two exceptions, the merchant in Emprise du Lion and the merchant in the Hissing Wastes. Those have valuable items that are best in class. Both require a Perk called The Short List, so pay attention to your Influence accumulation and Perk point allocation.
The Black Emporium and the merchant in the Descent DLC also have really good stuff. Those don't need the Short List perk.