Hi !
What is usually recommended is : 2-3% of your bunny weight of pellets every day, and 8% of your bunny weight of vegetables every day (and 3 different vegetables at least). If you choose to feed him only with vegetables, it’s about 10% of his weight everyday, with more dark green vegetables thant anything else (salads, aromatics, celery, etc …) and only a few root vegetables (I’m sorry, I don’t know what the right word is ; I mean vegetables such as celeriac, Jerusalem artichoke, etc …).
Of course, you have to introduce them one by one before giving the 8% to avoid any problem ; remember that you have to introduce salads and cabbages last because they’re not the easier to digest for a rabbit that never ate vegetables.
Right now, as you’re only introducing vegetables, you don’t have to give your rabbit less pellets, but then yup it will be necessary. Most of rabbits are so greedy then they would eat as long as there’s food ! ^^ And anyway, pellets are the thing they’re supposed to eat the less. 