Find some Petromalt for rabbits. It is a rabbit hairball prevention. Also, you can give him some fresh pineapple or some pineapple juice. The enzymes in pineapple break down proteins, including those used to make hair and fur. Papaya or papaya tablets can also help break up hairballs.
How long and how often a rabbit moults depends on its genetics as well as its environement. A rabbit moults at least once a year. The best show lines moult only once a year and for a fairly short period of time (2 months maximum to fully complete the moult). Of course, there are not many rabbits that moult like that. Some moult several times a year. Some take forever to finish out a moult. I had one that was in a moult at least half of the year. He moulted more than once and he held onto the moult for a long time. Lops (except english lops) have somewhat longer, finer fur than more short-haired rabbits, and the moult tends to be worse because of that.
Keep up with the brushing and put him on at least one of the three hairball preventions I mentioned above and he should be fine. Just watch for signs of hairballs, especially if he stops eating. As long as he is eating it is doubtful he has any kind of blockage like a hairball, but the hairs in the poop does mean he is injesting fur.