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I know it doesn't create redirects but I wanted to use it to figure out the list of files / pages to create 301 redirects for and then add these to the HTAccess file. However was I incorrect to just export the HTML files from Screaming Frog as there were only 500 of these but there are now 7000 404s in Webmaster Tools of PHP files.

I recently migrated a site from Joomla to Wordpress. In advance I exported the HTML pages from Joomla using Screaming Frog and did 301 redirects on all those pages.

However Webmaster Tools is now telling me (a week after putting the redirects in place) that there are >7k 404s. Many of them aren't HTML pages, just index.php files but I didn't think I would have to export these in my Screaming Frog crawl.

We have since done a blanket 301 redirect for anything with index.php in it but Webmaster Tools is still picking them up as 404s.

So my question is, what should I have done with Screaming Frog re exporting to ensure I captured all pages to redirect and what should I now do to fix the 404s that Webmaster Tools is picking up?

I'm getting very confused.  What is the important number regarding backlinks to my site?

The Moz number vs. Hubspot grader spits out vastly different numbers. For the particular site I'm trying to improve, I don't have Webmaster Tools installed yet (waiting for webmaster to do as it doesn't have asynchronous code on it).

Also apologies for novice question but I remember once being told that offpage SEO and specifically the amount of external backlinks is responsible for 75% of your SERP.  Is that still the case?