1. Somewhat agree. Does it need balance? Yes. Are "ground" effects bad idea in general? No.
One of the main features that Larian brought to RPG with huge success are environment interactions. It's also one of the things that gave new life to RPG games as it was good step forward and theirs sales compared to other classic RPG titles are showing it. Also making things 1:1 with tabletops/paper games for video games isn't good idea and rarely will work at all, so I do understand Larian decision. Some spells and skills with good RNG would be just instant kills, close to it or just too off for video game.
Overall it's good idea as it makes game more modern (physics and other new solutions) and gives new ways to use some spells witch otherwise would be boring, too situational to use or just too much RNG based. I would say it just needs better balance as like you mentioned some effects are just too strong/strange at the moment. One way to balance it might be setting not book AOE/Ground spells to have no "splash" DMG and just chance to ignite/froze, etc things. For example Fire Bolt would just have chance to ignite objects/enemies on direct hit with guaranteed ignition on flammable things like alcohols/webs (so barrels with alcohols would just burn for long time making it extra light source or something to throw/kick at enemies, etc) and explosion only happening with things that makes sense like black powder or some alchemic potions and so on. What I'm saying is that effect/combination for "No book AOE/Grounds spells/skills" should be small bonus dmg (like up to 25%, like electrifying water dealing extra 1/3 dmg + effect chance and so on) or outcome for you instead of it being the main way to deal with enemies. Also you can set it like 1st turn/step in fire haves lower chance to set "On Fire" status than every turn/step you stay in it after that. So in general I would say it's mostly matter of balance.

2. Most important thing to say for me, it's a bit too early to complain about that too much when there are still missing classes, subclasses, spells and skills. It's something to think about after future patches with content so probably about 6 months or so from now as it's mostly related to balancing the numbers. However, once again making it 1:1 with 5E rules most likely will only hurt the game. Having turns in which both your party and enemies miss everything constantly will just take out fun factor from it. This is why most other titles force active pause, so constant missing can be hidden in 1-6s turns. They probably can make like Classic mode with 1:1 rules, but it would be played by some small margin of players in the end.

3. Too be honest I don't see any good reason for it. It's good start, something bit different to others titles. It's not like our character and origins characters have any impact on these events, they are just trying to survive this mess and it's good. It also matches theirs starting attitude towards player as it isn't standard party of adventures established in traditional way. They all are just random people who want to survive, so sticking together and using others seems like good idea. Only thing I would change is adding Force Turn Mode tutorial where you need to sneak around/by some powerful enemies to survive and just reach next part of the ship and failing it would mean instant death from some bad ass enemy/monster.

4. This one is tricky. Most games end up with using it as a way to just add some potential extra line to pick up in the dialogue. Too be honest I will prefer if Larian won't use it and instead will focus on making our decisions having bigger impact on the world and our character being recognize by those deeds. As for companions I don't like idea of them being stick with one Alignment for the entire game. I think our actions should lead to them potentially chaining theirs thinking (not 180 degree of course) if they stick with us, companions leaving if they won't agree on mayor things and of course some potential betrayals. I think good example here could be Shadowheart who seems like Neutral/ Chaotic Neutral opportunist character, so our actions could lead her to darker path or something more heroic (will leave spoilers for my EA feedback)

5. I'm D&D fan and same goes for previous Baldur's Gate games (1 and 2). However, if I must be honest then without nostalgic aspect it doesn't look so good any more. Baldur's Gate 1 just didn't survive time trials and now is just a good game with average story. Baldur's Gate 2 ends up much better, but still it's a relic of the past. Someone can say they are masterpieces that shouldn't be touch, but I call it no sense. If something can't be changed or improved in just 70 years old field (Video Games), then why even bother to make something new. That's why it's time to kill your heroes and move on. I get from where you are coming, but still tabletop fans are small margin compared to video games fans. Where video games are now bigger market than music, television and movies.