Thanks for the valuable input, I really appreciate it!
I re-did my deck to fit the sealed standard, ie. only 40 cards. I went with Mardu, and today we played at our house some ~10 games. Aaaand... this deck pretty much crushed my friends attempts at anything. I think he won like one out of the ten matches we played, and that was a game where I was starved for mana, I only got 3 mana in my opening hand, and no more for the rest of the game.
I would like to attend FNM sometime in the future, when I get the hang of the game a little better. There's some mechanics not in the PC version on these cards that takes some amount of games to get to your head around, how you should utilize them and when, like renown and morph abilities.
I am aware of rotation, and KTK wasn't really my first choice, my purpose was to buy fat packs of Dragons of Tarkir but the store didn't have them so I went with KTK instead.
But yeah, I think I'll stay on limited for now, maybe attending sealed tournaments. I have no idea about what the local FNM sccene is like, I know where they play and when, but haven't dared attend yet. Now that I have some games under my belt I feel a little more confident that I won't screw up royally during play.