You should start downloading and playing "Season 1 Ep. 1-10" -- which contains all the episodes from Season 1. Then you should download and play S2E9 -- which (although not named "Season 2 Ep. 1-9") contains all the episodes 1-9 for Season 2.
When it comes to the bonus content: you only need the two codes for Season 1 ("datass" and "2legs"), and for Seasons 2 you only need the latest code ("carol").
There will be a final episode 10 for Season 10 in the (hopeful near) future, but this will not add any more story, only voices AFAIK. So if you play Season 2, you should already have all the story.
Here's on more important advice if you're playing Season 2: the version linked in the OP is terribly bugged, and the fixed version never got shared unfortunately. But some fans have made some fixes, and I highly recommend to install those: see
here and
here.