1) Canon is one of the top DSLR camera manufactures in the world.
2) 550D is the one you buy because it has the 18.0 effective megapixel CMOS sensor and 1080HD video recording from 24p to 30p. Also it has the 3.0-inch (76 mm) 3:2 aspect ratio LCD monitor.
3) the EF-S 18-135mm f/3.5-5.6 IS is the good one for start point. By the way don't buy the other one (EF-S 18-135mm f/3.5-5.6 IS STM).
The idea for using more than one lens is to try to cover the all range from wide angle to telephoto lens. The one (18-55mm) you chose is the worst one.
If I were you I will take the canon EF-S 18-135mm f/3.5-5.6 IS first, after you can get use to all your photo equipment for while, I will recommend to get other good lens you can offer, like bigger Aperture (small number F2.8 or F4.0) or the fix focal length.