1) When it comes to the plants the stem looking plants should be fine floating as they can get enough nutrients from the water. However, one looks to be an amazon sword and they like to feed from their roots so i wouldn't recommend leaving that one uprooted for too long.
2)Idk anything about containment but sometimes it can help to use a piece of yoga mat cut to size of the tank to put underneath it. This will help it spread out the force of the water on the seams to not stress on side more than the other. Also always make sure your tanks on a level surface to prevent this as well.