Keep in mind, each base would normally have 7 elements for the players to research, but for this one-shot I reduced that number to six. That is, six elements to research for one base. These elements are the builder/owner (whether the base's owner built the base themselves or if they had somebody else build it for them), the purpose of the base (the reason the base was created), the inhabitants of the base (like if the base had any or not, if there were henchmen or security personnel, if the inhabitants there are robots or golems, etc), the contents within the base (the stuff that is stored in the base), its defenses, and the history of the base.
Honestly, I would prefer if the party decided to begin to explore the first base they researched because I'm not sure if everyone has the patience to research a bunch of potential lairs to have multiple options to pick from. Though I have no objection against making preparations for the base (though the character creation rules state that the Player Characters have Benefit (Wealth) at the start of the game. I'll probably have a benefactor provide the party with these things upon request).
As per the Base Raiders/Mutants and Masterminds 3e Conversion Guide, you get more accurate information with higher grade successes while you get partially incorrect information from lower grade successes when rolling skill checks against secret Difficulty Classes set by the GM.
I hope that answers your question, and sorry to take so long to reply.
Edit: I was in a bit of a rush writing this post, and now that I've taken the time to reread what I wrote, I realized I may have given a long-winded half-answer. So the party gets a general idea of what to expect of the base (based on their research and the roll of the dice), but you don't actually know about the layout of the base.