But John 6:66 (hey, I didn't label these things!) says many of His disciples "were not walking with Him anymore." The Pentecost upper room had 120, probably a fraction of the total. At least early on, there must have been quite a crowd following (literally) the rabbi. (Luke 14:25, Luke 8:1-3) Not just men, but also women. Sometimes Jesus talked to them all, sometimes to 12, or 70, or only a handful. The boat they have could have held a dozen assuming the boat had sides, so maybe the full boat image is still OK.
Guessing here: the 12 were always with Him, unless sent out; another 100 or so were consistently following Him around, including men and women; probably another hundred or two that went along part of the time, as their family and finances allowed. And in towns, as many showed up as would fit the venue, and then some. I'd guess that most paid their own way, but not all could.
Judas must have been a busy man.
On the road to Emmaus, I wonder if while Cleopas (=Clopas in many traditions) was saying "They had also seen a vision of angels who said that He was alive," his wife Mary was nodding vigorously.