I have type 1 diabetes, have since just after my 18th birthday 13 years ago. Mattanna has pretty much covered it, I am on the same system as him, one long acting insulin before bed and three rapid acting ones. You get used to it fairly quickly. You get pretty good at estimating how much carbohydrate is in the stuff you're eating to work out what dose of insulin you should use.
I carry some glucose tablets, and always make sure there are some in the car. People do sometimes say "Ooo I could never do all those injections", to which I reply "well then you'd be dead in a couple of weeks!". It's not a big deal really when you're doing it yourself.
It's only a small bit of the pancreas that goes wrong, the rest is still fine so it shouldn't make any difference to your immune system. However it's a fault in the immune system that causes it to attack that bit of the pancreas in the first place. The reason they tell you to have flu jabs is that it's hard to keep your sugar levels correct when you're ill - they go screwy and you have loss of appetite etc.