You mean lower offset!! LOL. The higher the number, the further under the car they will sit.

Are your Mo's 7x17? My 7x17 Pro Race wheels were ET35, so would have sat slightly further out than your Mo's, if they are the same size. I reckon you will struggle with ET40, especially if they are not particularly good in terms of caliper clearance. My current wheels are also ET35 and are 7x16 and I had to use a 5mm Spacer (actually only needed 3mm). The AP Calipers are a VERY similar shape to the Brembo's.

Also, if you go for a 16", it will need to be a 7x16 to be comparable in terms of offset.

As others have said, it really depends on the offset of the Bells and Caliper Brackets. You can put a deeper offset on the bell, make the caliper to suit and gain yourself a little that way. You don't have ultimate flexibility, but may gain a few mm's.