1. When do enemies expose their weak spots?
It usually happens after they perform one of their stronger attacks, so it's just a matter of observing and learning. However, there are a few special cases where you can speed up the process tremendously. Hit Darknuts and Stalmasters with a quick strike and immediately roll behind them. Zant only exposes his weak spot after you've successfully blocked a number of his attacks.

Should I get a WiiU for this game?

That's a tough map despite holding only a tier 2 weapon as a reward. You should use the wind waker instead of the rapier due to the recommended element, you should have at least the tier 2 lightning armor to reduce the damage taken (you can't afford to lose more than 10 hearts here), and your level should be at least in the mid to high 30s to dish out enough damage. If you don't meet all of these requirements, it's best to play something else and keep a note of the materials that you need for Zelda's lightning armors, so that you don't waste them on another character. I know that the temptation to clear an entire corner of the map is big, but the progress on the adventure map is never linear.

The general strategy is to go right after Wizzro and then Volga to wipe the biggest obstacles off the map. If you mess up and lose too many hearts, you won't lose that much time with a restart. The best way to handle Wizzro is to wait for his weak spot to get exposed while playing defensively, because running up to him and trying to get in a combo can and will end up with him throwing some fireballs right into your face; when he rotates to throw fireballs, you can roll right through them with the correct timing (there are invincibility frames during the dodge animation). Against Volga you should be more aggressive because your normal attacks can interrupt most of what he is going to try to do; it also forces him into his quick jump and stab attack that exposes his weak spot; roll quickly around him when he flashes and you should be able to avoid damage while getting yourself in prime position for an attack. If you can defeat both while losing six hearts or fewer, then you'll be quite good to go for the rest of the map. Not that it's going to be easy, but you'll have the toughest parts behind you already. Fighting the numerous gibdos shouldn't be too hard, but it's a busy map that requires a lot of going back and forth. The wind waker's YYYYYX combo (I hope I got that right) allows you to clean out fortresses quickly because the attack covers a wide area.