Yes I know by the Senate but that’s not my question. Are they all voted on as a slate (subject to a Motion for Division of course) or is each nominee voted on separately? Does the Senate do any vetting or is it mostly professional courtesy to vote for the new cabinet*?
*IIRC John Tower was a VERY unusual case. Part of the reason he wasn’t confirmed was he was a bachelor and dated different women. And he was (maybe? possibly?) an alcoholic. Seems like there were a few skeletons that his Senators knew about.
Each nominee is voted on separately, and they hold confirmation hearings just like they do for an appointment in the middle of the term. The hearings can take place before the inauguration. The formal nomination won’t be received until the afternoon of the 20th, but everything except the final vote in the Senate can happen beforehand. (Hillary Clinton’s hearing was on January 13th, for example. The committee voted to recommend her confirmation on the 15th, and the full Senate voted on the 21st, the day after she was actually nominated.)
Remember that the Senate needs to confirm more than the Cabinet. More than 4000 positions require confirmation.
Only the major ones - Cabinet and judges - normally get the full hearing treatment. The vast majority are approved by the appropriate Senate committee and sent directly to the floor for a full Senate vote. The committees can and occasionally do make an issue of a lower appointment. Realistically, though, hearings on 4000 people would shut the government down more effectively than anything else Congress has tried.