So there is no good answer to this question, or it would already appear in the larger build order questions on this site. Unlike the early game (which is well defined) mid to late game doesn't have an easy answer, and anyone who gives you a BO past 20 is a snake oil sales man.
Even in the Zerg question you linked the answer was: What ever feels best
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Let's look at some of the basic Protoss builds and how they progress:
4 Gate
Usually this build is very all-in, and you're banking on winning early. However, if you do enough economic damage with a 4 Gate, but don't win you can still be at an advantage. At this point if you pressure more you're going to end up against a higher tech opposing force and probably lose, so you can expand here and maybe add on a Robo or two more Gateways.
3 Gate
One of the great things people like to do with 3 Gate is provide pressure so that they can expand. This sets them up with a nice little force as they transition into the mid game. Once expanding there are some people who like to progress to 5 Gate + Robo, or 3 Gate + Double Robo, or even (recently) 3 Gate + Double Starport. There is even a nice 4 Gate + Robo to provide pressure so that Protoss can take a third expansion.
You probably notice a number of trends between these two builds, even though I picked two builds that could not be more different there were a number of important ideas:
- Your Production must be proportional to your Income. If you have less production than your income you need to have a plan for it (eg. setting up to expand). If you have more production than your income you need to be aggressive
- Don't over commit. When you're ahead, your number 1 priority should be to get more ahead (ie. expand)
- While you always need to tech (ie. Red Queen Hypothesis) teching takes time, so don't forget that in your calculations.
Now you'll notice that a lot of what's being discussed is Income vs Production and there are a couple tools you can use to help you out:
Remember: To get good at Starcraft you need to get good at Execution and Decision Making, not get good at following a road map.
The most effective way to level is to always do games that gives you exactly 50k XP points since you only get a fraction of the total XP you should get once you pass the 50k XP in a game (you get 67% less IIRC).
You can also try to cheese your way through since when you finish a game extremely fast, you get bonus XP for the game length.
Other than that, it's all about how good you play. The better your macro becomes, the more units you'll be able to pump out and the more XP you'll get. The better your micro will be and the more XP you'll get for killing units.
This guy here explain pretty well how the game length bonus works: What is the game length bonus?
XP charts for levels
Best Answer
One zergling take 0,5 supply (and this is the cheapest zerg unit) so you should have maximum number of 400 zerglings on map.
Expansion:
After my small 45+ Blizzard minutes research I gave up.
I played custom with very easy Terran bot. I focus on building Overlords.
As you can see; 342 (unit produced) - 21 (unit lost) = minimum 321 units alive in the same moment . I don't receive any waring or other information that I can't produce more Overlords. So... you can have probably max map number of Overlords.
Max map number in Starcraft II is (probably) 4096 so you can have max. 4096 Overlords.