If that certificate expires, you’d have to downgrade to Full (not strict). It will function with an expired (or mismatched) certificate. Better yet, get a Clouflare Origin certificate. They’re only good for Cloudflare sites, but they’re free!
https://support.cloudflare.com/hc/en-us/articles/115000479507-Managing-Cloudflare-Origin-CA-certificates
As for the not-secure fonts, that’s usually Mixed Content. If you post the domain name, we can help more.