What's the length of the hutch if it's 4ft wide?
I personally would not feel comfortable with Bruno, my french lop in anything less than 5ft either (even that would be a bit of a tight fit factoring in toys, food dishes, litterbox ect.). While I was waiting to get him neutered and move him into the rabbit room, he was in a 2.5 x 4.5 grid cage and even that was pushing it when he was only around 7 months, not fully grown. Could easily tell he wasn't happy with the lack of room. He is very energetic mind you. Loves to binky!
Also, how frequent would exercice outside the cage be for the future french lop? Or would the run be accesable all the time? Exercise would have to be quite often to prevent problems from not being able to exercise fully in a cage that size.
Bigger is definitely better if you can manage! I would just keep my eyes open for anything larger if you can. I am fourtunate enough to have an 8ft x 4.5ft pen for Bruno and his two girls, which he just loves the extra space.