If you already have the wheels, and don't plan on lowering the car then, bang them on the car and have a look. You might get away with just having your arches rolled because.....
I bought some et38 wheels a a few years ago for my IS200 and had rubbing issues. The car was lowered 30mm. I got the wheels on ebay so couldn't return then, so I started by getting my arches rolled. This helped a great deal, but because I was lowered, during hard cornering and dips in the road I still had rubbing, so (thanks to Gord) I got the alloys machined very slightly by 3mm, making the offset et41; I never had a problem since.
I know your wheels are 19" and not 18" like I had but because you are already have a et40 offset and are not lowered as far as I know, you might get away with just a bit of arch rolling...

As for thr Tyres - stick with Falken Fk-452. I use them quite happily on a much more powerful car and will soon have them for the Aristo too