Best disconnect the injector loom, no point spraying fuel about for no good reason, what else could go wrong?
Well you could drop a bolt down the spark plug hole, but that's easy fixed with a magnetic pick, everyone who doesn't own one, buy it now, they cost nothing and you'll wonder how you survived without.
The above leads to this, make sure you clean out any crap around the plugs before removing them, a good blow (teehee) should sort it.
Ummm... try not to cross-thread any bolts (incl. sparkies) when putting them it back in, always tighten with your figures first, then the ratchet.
Yes, rockers stay, only the valley cover needs to be off, the cross pipes can even stay if you have some extensions and uni-joints, it's fiddly but has worked the last few times I've changed spark-plugs and/or coils.