You shouldn't need to extend your wheel studs if you're not using any spacers.
My car is dropped 20-25mm and I've run 245 front, 275 rear with offsets as low as 20 for may years with no rubbing. If you you really want to max the drop and the width, i.e. 30mm drop and a low 12 to 15 offset with 255 and 285 tyres then you would be best to check if anyone else has done it, 25 to 30 offset would be safer with those tyres.
Also, if you decide on the 285/40 rear tyre you could consider 10.5" wide.
Your best bet might be to speak to one of the forum traders like Tarmac Sportz who can probably suggest and supply a good setup to meet your needs!