I would only suggest getting a translation based on the first English translation, the one by a freind of Hugo. There is an modern version based on that one...it has no pictures, but it reads like a Victorian novel...and Hugo was a Victorian-era writer.
The Bishop section clarifies quite a bit of what happens later, so it's worth skimmin deeply enough to understand the Bishop.
I skipped a bit of the description of the Paris sewers, but read enough to imagine that I could see and smell them.
Otherwise, just start. By the time you meet Valjean, you'll be well and truly hooked on The Brick. Then, when you see the show or its movie, you will mentally fill in the parts they had to cut but that the original french audiences knew by heart.
Just checked: I like the Lee Fahnestock, Norman MacAfee and Chris Bohjalian trans;lation, a Signet Classic. I wish it had had pictures, but it seems the best.