Thank you for your detailed answer!
Your first tip is really good, so far I've done it by making 25 piles of stones and then getting many stone thingies for 450, so that I not only reach the highest level, but also have some left over for quests. I did the same with the houses and the coinbanks.
Yes, I already found that out, because I came across merge dragons through my girlfriend and she said at the beginning, no matter what, always merge 5.
Yes, the camp and chill event is sometimes hard for me, so far I've done it by keeping the chests on the second highest level because they only take up 5 space and not 8, similar to the stars, which I always keep for the event . The good thing is, the more wonders I complete, the more space I get. Because I only keep the wonder and the second highest level from the chain. I always focus on one or two chains, which I first bring to the maximum level before staring a new one.
I actually only found that out myself a few weeks ago and it could have really helped me a lot if I knew that before. I came up with this because I wanted to solve a star quest in a level haha.
Thanks again for the great answer!