I have more than 100 domains, for which we will be installing SSL,
I have few doubts before we start on this
Can I add all 100 domains in one single account? or is their any limit to each account?
I see that it is free for a year, so I wanted to know what is the process after a year, will it get auto-renewed, or should we renew it manually? If so what are the charges to each account or domains?
On your server I presume? That would be unrelated to Cloudflare. You could use an Origin certificate issued by Cloudflare but the configuration itself will be still solely on your server and not related to Cloudflare.
Yes.
What is free? The account itself is not limited to any year and does not any renewal and the certificate is unrelated.