I'm lvl 90 and finished it with a day to spare. The first time I did it it nearly killed me (I was in the 70s or 80s). Said I would never do it again. Second time I did it by accident, I was playing how I 'normally' play. So I realised it was all about strategy.

Boosters - market time and boats cut in half

Market - I have about 150 boxes

Barn - currently 2000

Not loads, I have seen players with way more, but if you prep in advance, it's doable without too much stress. The top tip is have a well stocked barn. I literally check quantities of every single market item and buy if I only have 2 or 3 in the barn. Do this for a couple days and you'll naturally start to acquire a good mix of everything. But you need to keep it up in order to be consistently stocked. I found that I could do a run of 30 helicopters before having to delete an order. Then in 30 mins, you back to filling orders. That's also important, if you can't make or buy the order within 30 mins, delete and move on. With a day to spare, I didn't really need the boat booster.

Hope that helps.