I don’t think it’s redundant. Cloudflare will make less requests to the origin (Siteground) because of its cache. The Siteground cache will make sure that each time Cloudflare does hit the origin, the request is fulfilled as quickly as possible, resulting in a faster TTFB for the user.
The answer to your question about saving CPU and RAM usage is most likely yes, but it depends on several factors, like how many pages are being cached and how often they are cached and subsequently requested from cache. You can also consult Siteground support, they may have some stats to provide.
As for the TTL values you chose, I normally see people using an Edge TTL that is greater than the Browser TTL. The exact time depends on how dynamic is your content, how often you make content updates. You can’t purge browser cache, but you can purge Edge TTL any time, either manually via UI or API, or by using the Cloudflare Plugin or some other solution (there’s a combination of Worker and plugin for that too).
One last consideration is that, in case you want to make sure the Always Online feature works for your site, it has to have an Edge TTL that is equal or greater then the Always Online minimum cache values, which varies by plan:
- A “Cache Everything” page rule is enabled with the “Edge Cache Expire TTL” lower than the caching frequency (Free customers: 7 days, Pro customers: 3 days, and Business and Enterprise customers: 1 day). In this cache the “Edge Cache Expire TTL will cause the Always Online cache to be purged in the corresponding interval”.