Coop Advice

Hey everybody, I am a first time flock owner and I have four ducklings that are 13 days old today Im working on finishing their coop outside and just wanted some advice. There are spaces about 1.5-2in in some parts of the roofing as you can see in the pics below, should I cover these with hardware cloth or some other material? I've read some horror stories about racoons etc. Also I am wondering what type of bedding I should use in the middle part of the coop. I was thinking about putting in some larger gravel but I don't know how the ducks will like that. I am going to try the deep litter method inside the enclosed part of the coop where the flock will be at night as I am trying to keep cleaning down as much as possible. I also am wondering what you all think about the pool? I have installed a valve in the bottom that Im going to attach a hose to that will gravity feed down to my raised beds. Should I build some type of platform around the pool or can I leave it as is? Thanks for any advice, photos are below.

I use those pools for my ducks and geese, they last a couple of years and would last longer if they had a platform around them to protect the edges. One thing to be really careful about is not to let your ducklings in it until they are large enough to be able to easily get out. I also put a stepping stone inside. I prefer to use mulch in the run rather than gravel, and I think ducks will be too "wet" to use deep litter in the coop, but really haven't tried. Looking good

What type of mulch? Like wood chips? Or some pine bedding?