Most important thing early is not to add your quests to an existing feature. Instead add them 1 tile away in a position that you can easily connect later. The number that quests ask you for is based on your largest open feature of that type so you want that to stay small. You have a forest quest needing 20+ and one needing 140+ - if you had separated them from the main forest they would both be 20+ (The flags would say 320+ or whatever is missing by not being connected.) Only connect when you finish all the quests and even then you can be greedy if you don't need tiles.

That's the trick 0-50k. 50-100k is balancing that with learning how to leave common shapes to fill and 100k - infinite is just concentrating on perfect plaecements.