welcome to the forum pal. One thing you should never ever forget, you can use flating ans sinking flies with a floating line- you just have to change your terminal gear to suit.
8-9ft is great for small dries, as long as the leader is fine enough and your casting is delicate, but for a team of flies something a bit longer might be on the cards. you don't want your flies too close to the end of your fly line. And thats about all I know about stillwater fishing

mix it up and don't be rigid with your tactics.
As grouse would say, change your depth before you change your fly.