I wouldn't touch the kernel with a ten foot pool. I leave all that up to the developers. If I like what they've done when I load a rom, I will then usually donate to them to keep the good work flowing. I would highly suggest you do a lot of reading and getting used to your phone before you start flashing roms. If you aren't sure about something ask questions first. It will save you a lot of headaches down the road. Always follow instructions explicitly as they are written too. If you don't understand what they've written or how to do something, don't do it. That's the fastest way to brick your phone. That being said, flashing roms sounds a lot more daunting than it really is. As for different launchers, you can change those til your heart's content, you don't have to be rooted or anything to switch out launchers. Just remember, read first, ask questions second, flash third.