Do you want poop to fall through the floor, or not? Either way can work well, but they are managed in very different ways.
If the poop falls through the floor, you need a way to remove it from underneath, and you do not put bedding in the coop at all. The chickens walk on the bare floor. That is how the panels are designed to be used.
If the poop does not fall through the floor, you do put in bedding, and you replace the bedding at intervals (daily to yearly, depending on various other details.) Some people also scoop out poop in between the times they change the bedding.The chickens walk on the bedding and scratch in it, which makes a very different experience for them, as compared with being on a bare floor.
If you know which way you want to manage poop, you can more easily choose an appropriate flooring.
As regards sanitizing, that is important if you want to kill the old flock every year, then kill all germs, then bring in a new flock, which is common in commercial situations. If you are keeping the same flock, there is usually no need to sanitize anything about their living quarters. Remove obvious visible poop, keep it from stinking, and they will be fine. If the same chickens are living in the pen, they will re-populate it with the same germs anyway, so sanitizing is a waste of effort with no real benefits, plus you have the disadvantage of getting things wet. Chickens usually do better if you keep everything dry.
