My Suggestions:

Listen to At The Races with Steve and you'll get the verbal version of a clocker report for the Derby. He will frequently have Welsh and Gary Young on over the next two weeks. The benefit is you get the opinions of top clockers who've seen these horses train for the past year in most cases. Supplement with the Twinspires/CD daily videos and listen to some of the comments there. You'll have the Derby more than covered from these alone.

For undercard races DRF will likely have the most comprehensive resource and can be really valuable for multi race horse players.

If the Derby is a day where your personal handle is high you might want to be cautious with how you incorporate into your play if you've never used them before. Generally speaking, I try not to let them negatively influence my opinion but will use them to solidify and upgrade opinions.

As an example, Game Winner and Tacitus are notoriously average/bad work horses. Don't expect to be dazzled by either.