Fans are just like large mobiles. Kids love them. Think about it - half the time they are sitting in a baby seat or sitting on the floor - it's something to look at. They don't know what a fan is .. it's just this huge thing on the ceiling blowing air about. It's probably more interesting than looking at the toy block that doesn't do anything, right? :)
They don't respond on cue at this age. So long as they turn if you say, bang something loud, you're fine.
Usually kids who have separation anxiety are the ones who keep checking for mom .. if mine were content, they'd busily occupy themselves.
Sliding and throwing toys - mine did that until they were toddlers .. they make up their own ways to play with toys.
If you stack rings, at some point (when they are ready) they will be able to do it too. Some do that really early, some later, some don't find stacking them anywhere near as interesting as rolling them, chucking them, or whatever :)
The best advice I was ever given was to biff my baby/toddler books. When I did, I stopped comparing my baby to others. I trusted my doctor would tell me if something was wrong, and I listened to my gut :)
Sounds completely normal to me :)