Hi nessa,
La Ronde has completely transformed since I last attended back in the Summer of 2002. However, for all the times I went, the weather usually cooperated, but that's obviously something you'll have to check to begin with before you even consider planning your day there.
As for the rides, of course, you'll be intimidated by most of them at first, but that's the thrill of going there in the first place. I do recommend, however, that you ride whatever you feel most comfortable with and what you believe you can handle. I can't really say anything about the Goliath as I've never tried it, though I'm sure the experience is well worth it, given its current title in the nation.
With luck, perhaps you'll be able to witness some fireworks displays shortly after that since the date of the first entrant is indeed presenting on the 20th of June.

If the weather happens to be foul on the 15th (I can always update you with the specifics on this), then you might want to consider trying to go to La Ronde on a fireworks day to get yourself a double treat.
And I don't have any recollection of anything bad that happened at La Ronde recently.
Regards,
Trav.
