Need insight into W3 Total Cache

We have our site deployed on aws with horizontally scaling with EC2 instance behind ELB. Due to this we have our wp-content in EFS. We have over 100k user traffic on our site, so we need our site performance to be really good and need to be up for over 99.9% time. Following are our questions and issues:
1. Documentation suggests using “Disk Enhanced” for page cache. But when we do so due to EFS read slowness, we have to switch to Redis. Due to suggest using Redis for site of our traffic?
2. We have issues with images intermittently disappearing from our site. Support team noticed that when they went to admin panel and cleared the cache it used to appear. can you suggest what configuration could be causing this?
3. Support team generally goes and clears the cache for most of the issues. most of the time it works. do you recommend this practice?
4. We have not enabled Preload. One reason was we have over 3000 posts and growing, so we thought that it could cause DB load spike when cache invalidated. Is our understanding correct?
5. Do you have recommendations for Redis instance sizing for Page, Object cache?
6. We have noticed that our posts sometimes go to object cache and sometimes to page cache. what is the logic?
7. DO you recommend using CloudFront post caching for such high traffic site?
8. What is time take for pages to be cached again after clearing cache?
9. Is there any way to identify if a page is cached?
10. What is the advantage of running “wp w3-total-cache pgcache_prime” over doing from it wp admin screen?

The performance issues are very critical for our client’s business and there we will be open to subscrible for paid support to solve our issues. Please do let me know if you have such services. We would like to have a call with you if that is possible too.