Im not sure but if you look at the newest brochure on the official DLP site it might tell you when the summer season starts which would give you an indication of when they may start
Yes it is. Bastille Day represents when the republicans stormed the BAstille (think Tower of London - ironically there were few inmates) sparking the start of the French Revolution to dethrone the Royal Family and establish the 1st Democracy in Europe since ancient Greece and Rome.
The closest thing we have in the UK is Guy Fawkes night, which of course is a celebration of stopping this sort of thing (so British).
As for fireworks, you know you are pretty safe with anything after Bastille Day. Anything before varies, sometimes there is nothing, other times they have been going for a week or two.
I miss the Christmas fireworks they had until Jay Rasulo came on board