Improve slider performance

This is just my opinion:

1. The number of slides depends a lot on the file size of the slides but the number does matter. In my sites I try to limit the number to 10 or less.
2. There is no ‘standard’. The dimensions depend on your theme.
3. One important way to increase performance is to resize your images to the proper dimensions and quality. In general, try to resize the dimensions to the exact size your slider needs and reduce the quality of the image to get the filesize to less than 100KB (some developers recommend less than 50KB). See this article for my suggestions.