You played the first few D:OS fights, and then did Under Siege, but that mod is pretty short. It doesn't sound like you went back to D:OS afterwards. So, you haven't finished vanilla D:OS 1 on any difficulty yet?
If that is the case, then I suggest you play the EE on classic first and finish it before starting Tactician. I don't get the impression that you're quite ready to jump into Tactician.
Having finished the game and getting a solid picture of the mechanics throughout - that is the best recipe for success in Tactician mode.
Observations.
1. ...Does this matter? It does not.
2C. I recommend you do the Tutorial dungeon anyway, because it contains loot and materials which can come in handy. Money and supplies are in very short supply early on and every bit helps. There is some XP in the tutorial dungeon and you can reach level 2 before the Orc fight on the beach if you're diligent. However, there is something to be said for leveling up during a fight - it's a free full heal.
