I think, heads-up is a dying game format at least online. It has basically been solved as witnessed by an AI (artificially intelligence) poker bot beating the best human players the second time, an event was held.
If you look in the SnG lobby at
pokerstars you will see, that at the highest stakes, you can only play heads-ups, and there is always some shark sitting at each of the tables waiting for pray.
Typically the same player at the upper 2-3 buyin level, then another one at the next. And then for sure, if someone takes the bait, its a race between the sharks to occupy the first seat on the next table, that pop up.
This is so obviously not a healthy poker eco system, and I think, this is part of the reason why, sites introduced the lottery style Spin n Gos a number of years back. In these you cant see, who is already on the table, so sharks cant "bum hunt" recreational players and avoid each other.
Sure sites could do this without the lottery element, but since the whole idea was to make SnGs more recreational player friendly, it made sense to add that as well. And it also kind of masked, what was perhaps the more important move, to take table selection and bum hunting out of short handed SnGs.
If you are going to play tournaments, you obviously need to learn heads up, but I dont think, its the game form, you want to specialize in. It had its time, but the harsh reality is, there will never be another Doug Polk, now that it has largely been solved. Ring games are more complex and therefore have a better chance of surviving online, so these are, what you should learn to play.
I agree with those suggesting to start out with 2NL cash games, because cash is the simplest and most pure form of poker. When you are doing well there, and have learned the basics, the next move could be the 45-180 man regular speed SnGs on Stars. These are a great place to start learning tournament strategy.