But yeah, things like this put me off playing online. I'd have no chance doing this kind of optimisation 'on the fly' at faster game speeds, and adapting my strategy based on what the enemy is up to. I'm all well and good at planning, but when the game speed goes up I just fail badly and important things get forgotten.
Truth is, the players that can do this well are not the kinda players you will face up to online.
If you can complete these challenges, odds are if you start of with some custom games 2v2, and get a feel for the game that way, then move to 1v1 you'll likely do quite well.
The only 'trick' really, is to 'get lots of stuff and attack'. You would be surprised how many people try and build too many different structures, and forget to just build 'stuff and go attack'.
A good example, a couple days ago, I was getting cute against Terran, didn't really build much at all and he rocked up with a handful of marines and won. He wasn't necessarily a better player (although he could have been, the game was too short to know
) - he just built stuff to attack with 
. You really do have to be quite aggressive in this game.

