Assuming you have a lot of food, like a few million, the best move/gem ratio is the top tasks by skipping quests and the 150k feeding. I know, it’s tedious, but it’s almost 4 moves per gem wasted. If you are really grinding, you should also skip the 10 million gold with the 150k feeding. Basically the whole cycle you spend 5 gems to get 20 moves. The time management on this is way better than the other 3 tasks.
the second task you can do but the time wait with arenas and league and food makes it not time friendly. You can set up your food prior to going to bed to get it ready for the task the next day. Sometimes it’s better to spend the gems on reset the league if the timing is right, like you will have tasks of 2 leagues, then 3 afterwards, and you still have unharvested food. Spending 10 gems to reset league knowing you can get 40 moves is acceptable. Even a 3/1 ratio is acceptable..
The third task I don’t even bother. The fourth is pretty self explanatory, it’s a waiting game. Just clear your hatcheries and breeding stations. The sea/light I just leave the eggs there until all 5 are there so there are no accidents. While I’m waiting for those to be ready, I’m already breeding 3 of the 4 nature/war tasks. If you just wait these out, the ratios are tremendous but again you lose a lot of time. If you speed the breedings and hatching with gem, it’s a 1:1 ratio. If you just wait these out, then you can manage 3 hatching and 3 breedings in one week, giving you 300 free moves without spending a gem.
So as far as 2 star costs, best estimate you need 8k items. Assuming average player can manage 2 items per move, u need 4k moves. If you follow the trick above and add in the free moves every few hours, you will average 4 moves per gem which means you need roughly 1k gems to get 4K moves. If you are really good at the puzzle , you can cut that by more than half.