To be honest I do think the Cech signing is getting a bit overhyped by Arsenal fans (moreso on other places), he's a good signing no doubt but in my view you already have good keepers, Ospina for example just look at his recent performance against Colombia.
In my view if you are serious about challenging title you can't go into a season relying on Coquelin, if he gets injured you're back with Flamini most likely.
You definitely need to still strengthen in a few key areas, striker, CM (guessing you've just been outmatched in fee/wages for Schneiderlin because he is exactly what you needed ). Still not entirely convinced with your CB situation either if I'm honest.