I would recommend a 10mm spacer. Tissimo and another guy with new wheels have 10 inch wheels with +35 and have been successful. When looking for spacers you want to keep in mind that you want a min of 8 turns on the lug nuts or else you need longer studs or spacers with the studs built in. Our cars came with hub centric wheels so this is what you want to try and accomplish with your new setup.
I'm not 100% on how to get the wheels to be hubcentric with spacers. However, without spacers you need a machined ring to fill the gap between the OD of the stock hub and the ID of the hole in the back of the center of the wheels.
Generally, after market adapters and spacers are lug centric and this is not ideal. If anyone has a link to some hubcentric spacers they should definitely post in this thread.