alloy change to 18

Hi, Looking for some advice regarding alloys and tyre sizes. Not going to lie completely clueless when it comes to this. The mrs owns a 2015 leon 1.2 tsi that has 16inch wheels on them and she is wanting some new alloys. She is looking to get 18inch alloys but unsure what size offset and...

replacing my standard 2002 LC 17" starfish alloys to a set of 18" X 7.5J, with an ET of 35, will these be ok on my cupra or will i have to use my 15mm spacers for a flush look?