Short answer: Yes
Long answer: Yes you can :-D
Why do ampibs have to be done before general combat? In theory combat is resolved simultaneously so order should not matter
i think that is just an artifact from the old revised rules. in rev, you resolved offshore bombardments first because the defending casualties couldnt fire back. now that they can, it makes little difference.
It was just a way to conveniently organize the rules, plus it keeps the resolution of the sea and land battles for each assault together.