What should I do with a mountain of data (like a list of ~25,000 potential keywords)?

Notes

EAT- Expertise, Authority, Trust
Do not rank for other branded keywords. This erodes trust. You’re trying to trick searches who are trying to find the other brand.
Sort and filter. The value is not in the mountain of data but in the final few targets.
Look into competitors to find even competitors who don’t seem to be competitors (like Nerdwallet vs. State Farm, since Nerdwallet writes articles about insurance and rank for relevant keywords)
Looking at keywords that competitors are ranking for but you are not can be noisy. You may be doing that intentionally or they may be branded.
Look at keywords to improve- keywords you already rank for but competitors rank higher for, rather than starting from scratch with new keywords. Find and fill the gap between your content and the higher ranking content.
You can use Moz Link Explorer to limit by a single page. Gives you a tight group of keywords. Still needs filtering but all related to a single topic.
You can cover a lot of keywords in natural language without traditional keyword stuffing
Figure out your next steps when doing competitive research
Don’t forget about other sources of your content (knowledgebase vs. blog)
Use unique, catchy phrases to see if someone is scraping your content or how quickly you are ranking
Consider 301 redirecting old posts to updated posts

Finding competitor content

Search <keyword> (site:competitor1.com OR competitor2.com) in Google.
Search <keyword> (site:yoursite.com) in Google to avoid cannibalizing your content.