As to the rattle - there are compartments below the trunk floor and on the sides - make sure nothing is loose in there befre you change the shocks. Make sure the spare is fastened down tightly. If one shock is shot, replace both sides or preferrably all four.
I have had great luck with Bridgestone tires on my various volvos and the prices at Costco (Price Club) are pretty good. What ever you do, be sure to have the tires changed at a place that is careful about torquing the wheel nuts properly. If they aren't done correctly you will end up with warped brake rotors in a few thousand miles.
By all means get the turbo leak fixed as soon as you possibly can - you didn't mention if it was on the intake or exhaust side but either can cause your car to run badly and wear oout very prematurely.