I know I can add few coats of sealant but how about polish? I'm not sure if I should add multiple layers of polish. I'm going to use Klasse.

Another question. I'm going to wait 24 hours before I add second coat of sealant but should I wash the car before I apply second layer of polish?

 

One layer of Klasse AIO is sufficient. You don't really 'layer' polish.

The car should be clean before adding the next layer of sealant. Depending on how dirty it got in those 24 hours you may only have to dust it or use a QD.

 

Polish preps the paint surface for waxing and/or sealing. Use it as necessary to remove minor blemishes such as clearcoat scratches and swirl marks.