It's changing finally, but it used to be that the French they taught in high school and college courses in the States was closer to the French of Balzac than the modern Parisian vernacular. There will be differences, to be sure, but mostly in the usage of words. You shouldn't run into much difficulty.
A novel is fairly ambitious for a first go. I would recommend starting with short stories and working your way up. Verne wrote short fiction, too, if you'd like to stick with him. Otherwise Maupassant is widely available, relatively easy to read, and quite rewarding.
Whatever you read, try to keep yourself from looking up too many words you don't know. One rule of thumb I learned was "Look up every third word; if you still don't understand, look up every other word." I sometimes deliberately read books where I don't have access to dictionaries to prevent myself from going to them too often. On the other hand, sometimes you'll have one crucial word without which a whole paragraph doesn't make any sense. But you can always come back and reread the passage later.
"Richmond is a real scholar; Owen just learns languages because he can't bear not to know what other people are saying."--Margaret Lattimore on her two sons