So as far as I can tell, your issues are completely avoidable by using in-game features. You know you can manually enter turn based mode at any point right? And that this does not put you straight into combat?

Scenario 1:

You get your party into position to start the fight. The guard leaves the room. You press SPACE and enter turn based mode. That guard will use his Round 1 Movement and will then stop until the game detects all your party members have ended their turn. You can literally go make dinner, come back, and he will still be where his turn's movement finished unless you ended all your party's turns.

Scenario 2:

You miss your first turn because you get a free turn when you enter the fight; as long as you don't just try to walk straight into it anyway. If you attack from range, or can sneak in avoiding detection, you get a free hit before you even roll for initiative. You do need to not stand in the middle of the battlefield, but it's very doable.

As a single example of both situations, take the adventurers at the ruined chapel. I generally have Gale and my warlock hiding behind the wall behind the archer, Astarion hiding behind the statue, and Shadowheart starting dialogue and the fight. I move my warlock up behind the archer to get a visual on the patrolling mage. When she is at the top of the ruin, across from the archer, I press Space and move my warlock back behind the wall. The mage is now fixed there until her next turn. Shadowheart starts the fight by walking up to Gimblebock. Everyone else is hidden. Hopefully she rolls good Initiative but if not she might need to tank a hit or 2. The mage will waste her first turn casting Mage Armour. My warlock will NOT cast Hex which will pull her into combat, but use Eldritch Blast with Repelling Blast to either knock the archer off his crate if he hasn't moved, or down the steps if he moved to get a shot at Shadowheart. The way is now clear for Gale to move up to the crate and Magic Missile the mage to death. Astarion then moves around the statue using Cunning Action:Dash to backstab whichever melee enemy is more threatening to Shadowheart. Shadowheart then Inflicts Wounds to finish them. Everyone in the party is now in combat, everyone in the party has made an attack action. Round 2 commences...


I haven't played DoS so won't comment on 3 & 4, but for this game just enter turn-based mode outside of combat and everyone is forced to use their movement, action and bonus action one turn at a time, whether they are in combat or not.