With any over-sized wheel, the sidewall of the tire is going to be a lot shorter to accommodate a similar rolling diameter. Any time you up-size wheels the ride is likely to suffer slightly, although completely manageable and should be expected with a lower profile tire. Spacers may be required but could not be determined by a car and a wheel diameter alone.
Spacers are used to adjust the offset of a wheel (how far it sticks out or sinks in from the side of the car) If you have more information on the specific wheels which you are looking at I'm sure you could approximate spacers/tire size etc to make them fit. There are a lot of factors that go into fitting wheels on a car and spacer size cannot be determined without the width of the wheel and offset of the wheel. There will also be factors like the tire size and ride height that will determine how much spacer you may need to achieve a certain look.