I've played a couple leagues. Yeah I think yhey are around the 7-8 week mark for length. I usually play a good amount in the first 3 weeks, maybe 2-3 hours a day in that time. Then once I start hitting the more grindy or difficult tasks, I sorta drop off.

Doing it that way I usually get 2 out of 3 of the cosmetic rewards. I don't usually get the outfit.

In all honesty, you dont have to worry about getting the rewards, you can buy them on the GE after the event, and any future league points that are earned can also be used to purchase old league rewards.

Further, you can "save" league points between leagues. I have like 13k points from the last one which should probably get me close to one of the new cosmetics anyways.

imo, just have fun with the league, dont worry too much about the rewards, they are easy to get even if you dont get enough points.