If you're making your own and using 5 gallon buckets, I think you'd need 4 buckets because you could only get 4 tubes in each. If you're making them out of a tote, it would depend on the size of the tote, but you could probably put 6-8 tubes in them thereby needing less of them. Not to burst...
Definitely block off the bottom because it's not really tall enough for chicken use but it's definitely attractive for rodents to nest. I'd put a cheap vinyl flooring inside to make it easier to clean out. The door being open and having the screen door is great for ventilation in the summer...