Need to understand how this works

I have a website that does from time to time have lots of traffic to watch a live show. So I looked at ways to help speed up the wordpress and cache was one of the things I needed to work on. So I added this WP Fastest Cache. I just noticed last week that my online store was having issues by not allowing items into the shopping cart. So I deleted the cache and it cleared itself up.

Here are some of my questions
How often do I need to run the cache Delete?

Is there be a automatic function for this?

Is there a way to block the shopping cart page from being cached?