Very often you won't get that upfront research because juniors don't have the knowledge necessary to even start looking for themselves. Because you expect them to come to you with evidence before they ask you, your devs will just avoid asking you and spend hours wasting time instead. Any minimum requirements are a barrier. Barriers are bad for learning.

You need to welcome questions even from people who have apparently done no research at all, or juniors will always worry that you'll accuse them of not doing the "necessary" work up front. If you're kind and approachable, and you don't tell people off for failing to meet your minimum requirements, you can guide them to finding it themselves.