How many are needed depends on the variety of things you want to shoot.
Because you're just starting out, the idea is to give you enough flexibility that you can shoot most things reasonably well with relatively little money expended. That's why I generally recommend that people who are new to DSLR photography pick up the 18-55 f/3.5-5.6 IS, the 55-250 f/4.5-5.6 IS, and the 50 f/1.8. I call this the "nifty trio" because they are inexpensive and optically good all at the same time.
Those 3 lenses cover an angle of view range from wide angle to relatively long telephoto. The 50 f/1.8 is a prime lens that will let you learn about shooting in low light and with shallow depth of field (the 55-250 will be pretty good at shallow depth of field as well when you shoot at long focal lengths and subjects that are somewhat close). They are all optically very good, so when you get your shutter speeds and exposures right, you'll be rewarded with rich, detailed shots.
The only reason I mentioned the Canon 17-55 f/2.8 IS in conjunction with the 7D is that one of the 7D's major strengths is its autofocus system that's useful for action, and the 17-55 has a significantly faster autofocus mechanism than the 18-55. However, upon reflection, chances are that if you're shooting action, you're shooting telephoto, which means if you get a 7D, you'll probably be better served with the 18-55 and a 70-200 f/4L IS.
Note that the 18-55, 55-250, and 17-55 are all EF-S lenses that work only on crop-sensor bodies such as the 7D, 60D, and Rebels. They will not work on any full-frame camera.
Again, budget is everything. If you're sufficiently budget sensitive, you will be better off with a 60D and more money for lenses than a 7D and less money for lenses, unless you know that you are going to be shooting a lot of action. Even then, the 60D isn't bad for action at all -- it's just that the 7D is as good as it gets for less than $3k for the body.
So what's your real budget here? With a budget figure, we can give you much better advice. Lacking that, all I can tell you is that if you pick up a full frame camera, you will need to spend a lot more money on glass to get the same capability as the "nifty trio" gets you.
when i first started looking for a camera i was planning to go with the sony nex-7 at 1369$ minus 25% off from employee discount at sony so i was looking at roughly 1100$ then i looked further into cameras and asked a bunch of people i know that owns cameras and they told me canon dslr so i looked into that and realized it would cost me somewhere between 1700-2900$ to start so i tried to find more options and ran into the fuji x pro 1 which is selling for 2000$ with a 35mm lens at B&H. so my budget went from 1100 to 2900$ back down to 2000$ the only reason i havent pulled the trigger on the fuji is because there is no zoom and alot of good cameras are expected to be released in the up and coming months. november fuji xe-1, sony nex-6 and then the canon 6d in decemeber...all within budget. i've put the dates in my calendar.