Certificate Issues with Mail & Safari

Hello,

As of yesterday I've begun having a problem with both mail and safari where I cannot access email or websites that require certificates. I'm getting various messages about SSL incompatibility or not being able to identify the website because of a cert issue. In full disclosure, I believe that I may have inadvertently click on a phishing email. I'm thinking I'm going to rebuild my Macbook Pro from scratch, but wanted to see if there is anything I should be checking first? Below is one of many pop-ups I get when accessing various sites (mostly in the Google family). A couple of pieces of advice:

1. What items should I check with regard to certificates?

2. Are there any programs recommended for checking system integrity? (I'm guessing this is beyond AV). I've used MalwareBytes on Windows, not sure if anything similar to that is recommended for Mac

3. I've already built a USB boot stick to re-install the OS, but I'm not sure of the procedure for data and application restoration. Is there a best practices document for this? I've got some critical items going on and can't afford extra time messing around with data loss

Thanks in advance,

Dave