1) Engineering is A LOT of work. If you are not prepared to do a lot of work don't look at Engineering. The subject matter itself isn't too demanding, but the amount of work needed to get good grades is tremendous.
2) If you enjoy math and science then Engineering is definitely one way to go.
3) I'm not sure if switching out and still graduating is possible all of the time. My gf was in engineering for her first year but she transferred out to specialize in chem. Unfortunately, a bunch of credits didn't transfer over so she was stuck in summer school for the past 2 years. Even with that, she might have to spend an extra getting all the required credits in order to graduate.
If you're switching from one type of Engineering to another type then it can be done without too many problems, but if you're switching your major entirely, be prepared to spend an extra year in school.
4) I am Canadian so I only applied to Canadian schools. I applied to 4 (Queens, McMaster, Waterloo and Toronto) with the intention of getting into either Waterloo or Toronto. The other two were back-ups. I ended up getting into all of them but chose to go to Toronto.
5) The fact that you know nothing about Comp. Sci shouldn't be a big issue. You can easily learn it on your own or take a beginners course that your university offers.
6) Your school should let you take electives that you want but there are a few things you should look into. I've heard that a lot of schools don't recognize minors that their engineering students get. For instance, if you want to minor is business and take the required credits the school might not recognize it. If that's something you're considering, make sure you check before you make a decision. Of course, they'll let you take those course but you'll have to pay for them and it will be out of interest. Also, see #1 above.
Edit: In case you're wondering, I'll be starting my 3rd year of EE in September.