Many have direct experience in the Watergate investigation, prosecuting Enron executives, and other very high profile cases. Legally, anything is on the table if they turn over any crimes committed by Trump or his people before, during, and after the campaign.
By law, they can cast the widest net possible, likely part of the reason Trump himself is so frazzled by this complex investigation. And the fact that Trump's own lawyers have warned Mueller to stay away from the President's real estate deals suggests they already know he's looking at them.
As I've documented here before, Trump may have been involved in money laundering conspiracies tied to Iran’s Revolutionary Guard (details here) and Russian mobsters in the Republic of Georgia (details here) and New York City (details here). Hopefully, Mueller and his people are looking into all of these matters and more.
Of course, when the team's next public move or batch of unsealed indictments will happen is anyone's guess. Complex criminal prosecutions take time and sealed indictments may already have been granted without the public's knowledge.