rare ferry
I wasn't paying too close of attention, just opening the game every 20-30 minutes to buy things and closing the game again. I think I was able to buy The Big Cheese before the last few in the screenshot, allowing me to activate Challenge mode without buying everything.
I didn't want to get flagged as a cheater so I waited until I had enough to buy everything before activating the challenge mode so I'm not sure what would have happened if I tried to do it early.
orchid nest
It's fine. That's not cheating. Every upgrade, like "The Big Cheese" has it's set requirements. Which is a price and certain pre-requirements to make it show up. You don't have to buy everything. Sometimes I skip something if it does not help me. Like the infamous cats in Australia with the cats exploration.
rare ferry
OK thanks! I always assumed you had to buy everything. Never liked buying the Housecats upgrade either.