What if during few few minutes the % of neutrons was different and there is absolutely no neutrons (and He) or the number of n = number of p (so all gas is He4)? My guess: 1. Universe without He would be no very different from what we have now, stars will be able to form, even there characteristics will be slightly different. After 1-2 star generations there would be almost no difference with what we have now, 2. Universe with 100% He would be very different, but there will be massive stars. These stars would use triple-aplha reaction from the very beginning.