They're pretty easy, just messy which causes them to be smelly. Just give them a good amount of space, food, and a water source. I suggest getting one (water source) that won't splash, otherwise it'll get messy/smelly. You can DIY one. Just get a Home Depot bucket or something, cut out a hole that's larger than their heads, but not too large (Sand down the edges, too!) and make sure they can reach it, and then fill it up! Splash proof

. Yeah, they can eat layer pellets. Chicken layer pellets are fine for them. I recommend a minimum of at LEAST 2 so they don't get lonely. I'd suggest an even number of ducks, but it's ok if you don't get an even number too. (Pool) Sure, as long as it's large enough. I got my ducks a doggy pool, but before that they had like a super small bucket thing that was like 1/4 of a foot deep lol. as long as they can bathe in it. Deepness doesn't matter, just make sure they can kinda dunk their heads so they can wash themselves. My doggy pool is one foot deep and they love it lol. Probably one drake to 4 females so they drakes don't fight. I have one male with 2 females, and that's fine too except one female kinda gets left out, but she still hangs out with 'em. I answered the chicken question separately, so you can go look at that. I totally suggest khaki campbells for laying ducks. Pekins are fine but they're not as energetic as khaki's! well, that's the case for me, at least. Not so sure about sicknesses, but look out for sticky eye(fur/skin surrounding the eye just gets kinda crusty and the eyes get watery; just gotta wash the crust away and ur good), and coccidiosis (parasite, treat with Amprolium). Um tbh i don't really know this one but I just feed poultry feed and leftovers which usually consists of vegetable and rice. Explained the medicine part already. And don't be sorry! It's ok to ask questions. It makes you look better, too! All you want is a good flock

I hope your flock does well!