Squealing brakes, that starts after you've been driving a while, and goes away when you press the brake is most likely sticking rear pads - very common problem on these cars.
Can't really help with the "scraping noise", but may be worth checking that the brake backplates are not touching the discs; this can sometimes occur due to a build-up of rust on the inner face of the disc, and they can also easily get bent (when changing the clutch, for example).
As for the vibration, I'm going to assume that the car is a diesel, and suggest that you have a problem with your inner driveshaft joint - this is also a common problem. The reason it starts after you've been driving at higher speed for a while is because the joint gets hot and starts to seize.
Finally, as others have suggested, you need to find a competent mechanic who is more familiar with these cars - this will save you a lot of time and money.