SwiftKey 3 is good. It replaces the stock keyboard. There's a 30 day trial for it so u can test it out if u like it or not. I bought it on my first day.
Try out either Nova, Go, or Apex launcher.
I use Nova but the others are good and it's personal preference. It replaces touchwiz do you can add or take out as many pages u want, dock scroll, scrolling effects, resize icons, touch effects, and other sh*t.
I highly recommend it.
To make you phone load faster through different apps when hitting he home button go to S voice and uncheck "Launch S Voice" which is the setting to launch a voice by hitting the home key twice.
Then go to system settings>developer option>and go into Window and transition animation scale and put them both to ".5x"
Your phone should now launch windows and other sh*t as fast as possible now. By default it should be at like "1x" but ".5x" is the fastest.
Widget locker is nice to change you lock screen as well.