I know grad schools usually need three recommendation letters, and I think I have a good three from my department lined up (I haven't asked yet though!). However, I could also add a 4th one, as the professor offered to write me one (more as a character reference though, and not really speaking to academics/research) - is that okay and not overkill? Some more info: the 4th recommender is outside of my university (and outside of my field), but he is a fairly recent Nobel Laureate and is a well-respected researcher in his field! Thanks very much!