why would you need limera1n if you're on 4.0.1? That's already been jailbroken with star (jailbreakme.com)
update to 4.1 and use limera1n or greenpois0n.
use tinyumbrella when restoring to 4.1 if you need to preserve baseband (if you unlock with ultrasn0w) otherwise there's most likely going to be a baseband unlock come 4.2 in november. if you don't need to unlock then you can forget this step (though having an unlockable baseband increases resale value)