Their plan was to listen to what their enemy was doing in the campaign. They had to have a cover story for listening to the opponent. They needed to know what the Trump campaign was doing/planning. Unfortunately, Trump wasn’t doing anything special. He was being himself. They assumed they were going to win. So they did not cover their tracks until after. Then that stupid guy from Minnesota made a big deal about Russia Russia Russia. You see where he is now. (Franken)
That's a reasonble assumption, but doesn't spell out the plan. The Mifsud / Papadop encounter on March 14, 2016 was a nothing meeting as the indictment / plea acknowledges. The April 26th meeting where Papadop was told about "thousands of emails" and then subsequently "repeatedly sought to use the professor's Russian connections to arrange a meeting" seems like a weak case for spying in 2016. The plea looks a lot more like part of a maximum pressure campaign in January 2017 to get Papadop to flip and make up some charges on alleged coverup. That lasted until October 2017 meaning it was unsuccessful.
Then there's alleged Carter Page Russian involvement that we know was used along with the dossier to obtain the FISA warrant. But again that seems more like an FBI CYA policy than campaign spying. If they wanted to know about Trump they just needed to watch his rallies on C-Span. And Carter Page was not charged with anything. And it now seems obvious that the FISA warrant was used for spying on the Trump transition, not for "knowing what the enemy was doing in the campaign" but for prosecuting the enemy, perhaps as part of the "insurance policy".
In short this looks as well planned as Watergate (that is to say, NOT), and the spying and prosecution has also been following the Watergate template to prosecute a coverup. But there is a lot we don't know like whether Mifsud was part of a MI6 plot to plant dirt or misinformation or something. It doesn't appear to me that Mifsud was part of a coherent plan to listen to the enemy. I'm not saying it is impossible, just not a coherent plan with what we know so far.