When I signed up to CloudFlare I noticed that a lot of our site’s existing DNS records were not imported to the CloudFlare portal. Is there a limit on the number of records per domain or can I add the records that were not imported manually?
Cloudflare does a DNS scan of the top ~1600 DNS records, mostly as a convenience factor for smaller/ simpler domains. This can absolutely miss records for domains with any complexity. I’d recommend using the advanced function to import a BIND export from your current DNS provider or you can enter them manually if there aren’t too many of them (technically you can also script against our API but for a single domain is probably more trouble than it’s worth).
There is a limit per plan type to maximum number of records, but it’s in the thousands even fro the free plan. So start with the BIND import and then if you do hit the plan limits, support can give you guidance on appropriate plan/ limits for your needs.