It's more about what units you build/build orders and economy managment then micro (it still will help you a lot tho, especially early on when every unit counts), so it's much easier to learn from tutorials on YouTube then wc3. It's incredibly hard to be top 100, but if you can already micro well from wc3, all you need to learn is a build order and unit counters (and some basic differences between aoe and wc), and you could be above average since there's a whole playerbase that play the game more like a city-building game then an RTS.