Agree with almost all of this, from an immersion / balance perspective rather than D&D one.
1) Often there's a reason for the barrel placements that may not be obvious on the first playthrough. What if they toned down environmental effects - reduce down to one turn damaging effects, three turns debuff effects. For spent fire could have that become embers which function as candles and cause difficult terrain.
2) The game should also not permit jumping when in difficult terrain, currently you can jump out of ice / grease with relative ease (and the AI does not make use of this)
8) Perhaps a separate "shove" and "knock down" bonus action / action (shoving in the current implementation is really fun)
12) Disagree with this one actually - removing fast travel and waypoints would negatively impact gameplay experience. If the justification is to make it a 5e simulator then that's not a good justification
14/15) On my second playthrough I managed to do Act1 only resting three times. There were some weird side effects: like dialog lines happening that made no sense without the Illithid wet dream, and references to camp actions that hadn't happened yet. In any case, it's definitely do-able if you ration spells and scavenge food. Think the concept of campfire provisions could be experimented with - items that either need to bought at a cost from traders, or gathered as main quest rewards
