Welcome to LOC.
Nice car by the way, and hope you will enjoy it.
Re what is the best tyres, I believe there are few posts in the IS250/220 section and the Wheels and tyres section that compare different brands and other owners own experiences and reviews.
Shop around in the net, and you will be able to get good prices (but I am afraid you will strugle with your rear ones as they are 18/255/40, and they are only few out there, unlike the fronts).
Best of luck. :)
Ahmed