OZ Ultraleggera 18 x 7 with 215/35 tires, 42 offset will I be able to add 5 mm spacers without rubbing and without trimming?

 

Yes

 

Yes

 

If not lowered, you should be good.
If lowered you might get a little rub in the rear.
I have 18 x 7 with 52 Offset and 15mm spacers which would be equaivalent to 5mm spacers and 42 offset. I am running 215/40 Toyo T1R tires (only slightly taller than your 215/35. I am using a JCW suspension, so a little lowered. I get rubbing in the rear over some bumps especially with extra weigt in the car or some g-force in a corner. The outside edge of the tire rubs on the rear inner wheel well liner. A little trimming of the wheel well liner can correct the rub.

 

Oops I forgot to mention, lowered 1" on H-sport springs. Any one with that setup with pics to see if its worth doing aesthetically. I painted my arches so if I had to trim them the paint may start peeling so I dont want to have to trim. If its going to be a touch and go then I'd rather not bother.

 

Lowered an inch you will probably get a rub but it will probably not rub on the wheel arch, it will rub up inside on the rear plastic wheel well liner.
My previous 2003 MCS with 17 x 7 with 38 offset (almost the same offset as your 42 with 5mm spacers) running 215/40 tires and lowered with H&R springs rubbed in the same spot in the wheel well liner.
You will have no problem on the front.

 

I ran 18x7.5 ET42 on 215/35/18 with H-sports and only rubbed on big dips in the road with people in the back seats... FWIW, that leaves the wheel/tire sitting 1-2mm further out (and even more inside) than the setup you want to run.

 

As others have said, you should be good, and your red arches shouldn't be at risk. However, I have found that the variation in fit of the fender arches is often much more than the 1-5mm people are talking about in spacer and ET width. It also depends on the profile of the tires you use--they vary quite a bit for the same nominal sizing. In the end, it comes down to your willingness to accept the risk that the cool wheels and tires you want will rub a little on large dips...or not.