You're very
very wrong. It already exists here (and in Belgium, incidentally). What makes you think that normal observants of Sharia don't follow it properly thereby agreeing to heed the laws of the land? I'd suggest that you don't really know what Sharia law is.
I agree absolutely, that's how Sharia law works.
Yup, no problem with that either. If you're from a certain culture you might want a particular type of contract (as you suggest) and you might want to divide things according to certain traditions. That might mean a contract under Sharia Law, of course, no problem with that. The details are still judgable in the country's own courts, of course, because that's how Sharia works.
Yup, if I need halal then that's exactly what I do. We still agree on that aspect of Sharia law.
Nobody makes contracts "like everyone else", every contract has the scope for difference and specificity. If you want a particular type of contract then go for it. We still agree on the use of Sharia law in that case
They live by it every day, it's just how it is... think of Christian Law as the 10 Commandments. The media's idea of "bringing in Sharia Law OMGZ!!" really is suggesting that some kind of lawless Anony-stan government is going to take over, and that's just bollocks.