This is an event that I have attended regularly since 1985, probably going to at least 20 of the years since then, often on multiple days.
I have seen practically all the great players here since then (except McEnroe) up and very close. What is amazing about this tournament is that it is typically possible to see your heroes from a few feet away, and trust me, I have seen everyone play. Additionally, I have brought dozens of people along and they all agree that this is a special event.
Caveat--I only attend the tournament on the Sunday before it starts, perhaps the Monday or Tuesday early rounds. Have only gone later in the week once, and did not enjoy it as much.
The reason to go the day before the tournament starts is that all the players in the first round (except for those who make the semifinals in Toronto) will be there practicing. You can see the practice schedule online, or get it on arrival. Practically everyone will be practicing Monday and Tuesday as well, but this feature of the tournament diminishes as the week progresses.
In the old days there would be a very small crowd watching practice--there could be 5-10 people watching Becker, Edberg, Courier, etc. No longer. Crowds have grown exponentially, so you have to fight your way to the front. The best place to watch by far are the four adjacent courts on the south-west side of the complex. Walk to the middle, and you will have two courts on either side of you, and you can literally see the action from a few feet away.
It is a mistake to think that the top-ranked players are the best to watch practice. Nadal, Djokovic, Wawrinka train hard, but the Fed usually just messes around--when he turns it on, though, if you are lucky to be there, he hits some of the most amazing shots you will ever see. The guys training the hardest are typically the also-rans ranked in the 30s or so, of the younger up and comers. This is where the true action is--a lot of these guys have beautiful, clean strokes and amazing athleticism. Go see guys like Fognini and Lopez who are true entertainers. The ladies tell me that they all have great bods--a real plus given that they typically take their shirts off. There are also the tall, big servers, like Anderson, Isner, etc, who practice serving a lot, and who are truly a sight to behold at ground level.
Even bigger bonus are all the former greats who coach the current crop--you can see them all hanging out by the fence where you stand. The best to go see is Carlos Moya, wherever he is, because he has an outstanding collection of tricks that he loves to entertain the crowd with.
Don't waste your time trying to talk to any of these people--the pro tennis scene is as giant collection of assholes as you will ever encounter. Just enjoy the tennis.
If you want to see the players at an even closer range, stay at the local Marriott--which is where the vast majority are lodged.
Plenty of food options--much better than in the past. Lots of gear on sale. Food, merchandise, and drinks are expensive. Until last year the best deal was to buy the lemonade drinks at the various drink stands around the ground, which were large and delicious. Alas, they changed the formula and these are no longer good.
Sun--it's hot and not much shade anywhere. You have to come prepared with hat and sunscreen or you will get burned. For the same reason, I don't like going to watch matches on center court, which is a giant brutalist furnace of unshaded concrete. Why they cannot shade this for the benefit of everybody God only knows. Only go there for the evening sessions.
In short, an awesome sporting experience