1. Should I download the newest version of Joe? I haven't played the earlier version completely.
Yes. Newer versions have usually improvements that affect also earlier levels, so it's recommendable to download always the newest version, even if you are playing just the first levels.
2. Are there hidden levels in Joe?
No, but there are other hidden things. Try for example pressing the
cursor down and then the character '!'. Or try typing the word
'arkanoid' during the game.