Hi. Battle pass designer here.
There are 64 weekly missions, each awarding 10 stars, total 640. Each day you get 3 daily missions, each awarding 2 or 3 stars, total 2.5 (average stars per day) * 3 (missions per day) * 8 (weeks) * 7 (days per week) = 420 stars. 640 + 420 = 1060 stars. The pass has 80 tiers of 10 stars each, so it requires 800 stars to complete.
Also remember you can complete weekly challenges at any time, you don't have to complete them in the week they become available.
If you get unlucky and mostly get 2 star missions, or if you buy the battle pass after week 6, it may be impossible to complete. This being the first battle pass I'll be keeping a close eye on this. Please forward me any feedback you have. :)