Q1: You change the setting in the launcher to hide the statusbar. Since you flashed AOKP, it comes with Nova Launcher by default. Within the Nova settings, there an option in 'Look and Feel' to hide the notification bar.
Q2: Now that I mentioned Nova launcher, I'm actually using a different launcher that provides a bit more features. The launcher I'm using is Apex Launcher:
https://play.google.com/store/apps/details?id=com.anddoes.launcher Not only can I hide the statusbar, but I can use gestures as well intiate an action. In this case, I swipe down on the home screen to drop down the notification drawer.
Q3: Removing the persistent search bar does create more space, but increasing the grid size will give you even more space to layout more icons and widgets. This is an option that's available within the launcher settings. In my current setup, I have the grid set at 5x7.
Congrats to successfully rooting your phone and flashing AOKP. Play around with the launcher settings, as I think it's the first step to customizing your home screen.