"Rookies" in this case means the non-ikusei draft picks from last October's NPB draft which isn't necessarily the same as all the players in the Pacific League that qualify as rookies this season (i.e. were drafted before 2018 but haven't played much at the ichi-gun level). The term in this case also doesn't include a certain gaijin who signed with a PL team as an amateur this season. As I said about last year's set - think of it as half the Rookie Edition set.
The set has 44 cards - all player cards. Like last year's set they've got a bit of a high end feel - they're thicker than standard cards and they have shiny silver borders. They scan better than last year's cards did. The cards feature a photo of the player superimposed on a background that has one of the team's colors at the top that fades to white at the bottom. Pretty much all the poses are the usual "pitchers pitching, batters batting" shots - I think there's one photo of a runner running. Here's some example cards:
You can see all the base cards here and some of the premium cards here.