The limit is actually 8192 entities. My current map is at 6764 entities, and it is a rather large one. The limit has been reached by multiple released and WIP maps. With regards to your ideas, most of those things can be done, just be aware that there is a point in making a mission where there is a huge spike in difficulty - you have to create new assets, become skilled in multiple fields at once (e.g. scripting, not quite the same as building terrain). My advice is to start on a relatively small scale, and build outwards. You don't need to make a small and unambitious map first, because a lot of people have started with complex and very advanced projects (see the recently released missions, Moonbo's Requiem, or Kvornig's map). But before you plan out a huge, multi-mission campaign, learn the basic functions well, and release a single mission of, say, medium size and complexity. Afterwards, you will know your strengths and weaknesses; and you will have learned enough to make building the next mission even better.