We've a WordPress blog and had disqus plugin in stalled for several months. Around late August this year, the plugin created a ton of URLs that linked to non-existent location on our website. For example -

Correct URL: domain.com/correct-URL/ Disqus created -

1. domain.com/correct-URL/344322/ -> Throws 404
2. domain.com/correct-URL/433466/ -> Throws 404

So essentially, Google found a LARGE number of broken links that pointed to unknown locations on our own domain.

As the count of those errors (404) rose, our site suffered massive drop in traffic and crawl rate dropped to 10% of what it was earlier.

I wish to know -

1. Can large number of (we've over 99k of them) internal broken links cause rankings to drop?

2. I've fixed the issue in one go by creating 301 redirects for each bad URL to correct URL and removing disqus. Google however drops the count by ~1000 daily, as I mark errors as 'fixed' in Google Webmaster Tools. Is there any way to speed this up?

3. Should I setup custom crawl rate to 'Fast' in GWT to make Google crawl our website faster?

I'd appreciate your inputs and experience sharing.