You’re correct in assuming that the scrambling happens at the end of the Combat Movement Phase (8.6). Given that fact the planes would have already moved before the rolling begins and thus the bombing of the airbase would have no effect on the scrambling ability.
@mike141500 I believe that unless it says so, there is no limit on how many a nation can field. Just like all other units, there is not an upper limit. While there may be per turn limits, there is not a per board limit.