Hi,
I'm glad to hear that you've got so many sprouts to plant! That'll be an impressive future stand.
To answer your questions:
1. I don't have any personal experience with the Plantra tubes, but a quick Google search showed that they would probably be effective at protecting your trees. When looking at tree tubes it's important to consider a few key components, like stability of the tube and ventilation. The tubes we recommend are structured enough in our experiences that they won't fall over on the tree when staked down and they have air holes on the sides of the tube to let the tree "breathe." If the Plantra tubes you're considering meet these standards then it is likely they will be work well. The other thing to consider is height, as you want to keep the deer at bay, but at 71" the Plantra tube is more than tall enough. I usually use 60" tubes, which is the shortest height I recommend.
2. You're right in saying you should keep the tube on until the tree is going to outgrow it. More specifically, you should keep the tubes on the tree until the trunk is strong, and you can test this by gently pulling the tree towards you. If it has no resistance to you then leave the tube on, but if it feels sturdy then it could be time to remove the tube. If you take the tube off before the trunk reaches a diameter of 4" you may want to buy a bark protector to keep the trunk from damage by buck rub. And of course, you want the tree to be tall enough that it will be safe from deer browse.
Sprouts will need pruning when inside the tube, and you can handle this differently based on how big your tree is. If the tree is small enough for you to slide the tube off and back on without causing damage, then that will be easiest. If the tree needs serious pruning but it is too big to take the tube off, then you can cut the tube off the tree, prune it, and replace it with another tube.
Just in case you haven't seen these already here are some MyWoodlot links you may find helpful:
Installing tubes-
http://www.mywoodlot.com/images/supporting_information/installing_tree_tubes.pdf
Protect planted trees-
https://www.mywoodlot.com/index.php?option=com_zoo&task=item&item_id=619
Maintain planted trees-
https://www.mywoodlot.com/index.php?option=com_zoo&task=item&item_id=620
Good luck with your trees and let us know if you have anymore questions!
Jessica