I'm already limiting pellets [or so I thought], but I have an English Lop and they are prone to obesity.
I used to have a French Lop and we gave her unlimited pellets with no problems. For many rabbit breeds you won't have to. I would say just free feed and only do scheduled/limited feeding if they start gaining too much weight.
I am going to start introducing fruit and vegetables for Michiko at 4 months old. You should never give vegetables to a rabbit under 3 months old. After that you can give it a try, but do it very gradually so as not to upset their sensitive digestive system.