since no one has answered your questions, I'll try to.
First I have to ask you, what made you decide to get a monitor? It seems you haven't researched it very well, so a monitor may not be for you. They usually require a lot more effort than you'd expect, but if you are dead set on getting a monitor, I'd start with something small like Varanus acanthurus ('ackie).
Now, for your questions:
1: How long do they live?
It depends on how you look after them. Monitors can live for two weeks or thirty years.
2: What do they eat?
That depends on what type and size of monitor you get. Small ones eat insects, huge ones eat rats or rabbits. Most of the inbetween ones eat mice. Babies of almost all will eat insects and/or pinky mice.
3: What size tank do they need?
That depends on what type and size of monitor you get. Ackies will live in a four foot trough, big monitors need a whole room.
4: Which monitor is the one that is black with yellow dots?
Many monitors are black with yellow dots. Almost all of these are unsuitable as a first monitor. V salvadorii is probably the one you are thinking of, although V indicus (and a number of other Indonesian species), young V niloticus and V salvator are usually black with yellow dots as well. None of these would be a good first time monitor.
5: Are they aggressive?
Define aggressive. Some are defensive, some become relatively calm around people. If it needs to be calm, either reconsider getting a monitor or stick with the smaller species (such as V acanthurus) because no one can predict how they are going to turn out. At least with the smaller species they do less damage if they do end up being bitey 
6: And any other info i should know?
Yeah, lots of info you need. They need a choice of hide spots and plenty of things to climb on, hide in or dig under. Deep substrate, such as soil or leaf litter (depending on species), but not astro turf or newspaper. They need a hot basking spot, around 130F on the surface (not air temperature), but they also need to be able to get away from that hot end. They are active and eat more than you'd think, for a reptile.
Most importantly, do a lot more research before you rush out and buy one.