Seasons are yearly categories that each video is put into to determine when they were uploaded. 2020 was Season 0, 2021 was Season 1, and so on. The show technically started in Season 0, but most characters refer to Season 1's pilot as the "actual" start, although Dino needed to tie up loose ends as it relates to Season 0.
The full runtime of the show up to and including the latest video is 4:20:22:39.
Tommy seems to appear a certain amount of times per season, depending on the season's number. For example, he only appeared once in Season 1, twice in Season 2, and three times in Season 3.
According to Dino-Weapon, he was initially scared for Season 4 since he feared that there will be a major OOU event that will prevent The Editor from working on the show for some time.
This was actually his concerns with The Editor going to college, but everything worked out in the end and Season 4 ended up being much more successful than Season 3 in particular.