Survival is not exploration. Resource tracking is mostly survival, making discoveries is mostly exploration.
For light, it specifically notes that having a light source of any kind draws the attention of certain creatures, and it does! A creature with darkvision may have not seen the adventurers until they were within 30-60ft of them, but now the adventurers can be seen from miles away and an ambush is more likely. Turn off the lights and you're less likely to have that problem.
Tenser's doesn't really "solve" the bridge problem since the caster themselves don't benefit from it. They'd either have to physically cross the bridge themselves somehow or fly across, using resources. If the wizard falls off, the disk does as well and everyone begins to fall to their death. Its a risk that may or may nor succeed, not an instawin.
If the entire party is getting on the disk, its likely they'll exceed the 500lb weight limit. The least we can expect is that 3 people by themselves will weight around 300lbs and its likely between the gold and equipment they have that you could have a bit more than an extra 200lbs.