Hi Fubra!
There are some things to say here:
- Google can handle up to 5 redirects, so if you are under that number, you are fine.
- Serving 404's to google is not wrong neither will impact negatively in your rankings. But only give google a 404 only if that's the correct answer to the user.
- GoogleBot re-crawls from time to time every URL that has discovered in your website lifetime. The only URLs that will not re-crawl are those that you served a 410. HANDLE WITH CARE, 410 are too powerful.
- Redirects and DA are differents things. Dont know the new Mozscape Algorithm, I do not think that redirects would impact negatively in your DA. Focus in trying not to get GoogleBot angry or close some doors.
That said, my advice is: Crawl, scrape or manually get all those old URLs and analyze them. Then decide, whether to: 301, 404 or 410. Also, I'd give a little time to create a really powerful, interesting and userfriendly 404 page, so if some user land there they can keep being in your site and there is no bonces.
To back what i'm saying about how many redirections, Matt Cutts said it in these videos:
Can too many redirects from a single URL have a negative effect on crawling? Is there a limit to how many 301 (Permanent) redirects I can do on a site?
Hope it helps.
Best Luck.
GR