Start with season 1 (0.4) any file will do, don't get corrupted, don't worry.
After you have finished season 1 you can download 0.5 for free, or 0.6, but you have to pay for it as it is the latest version. When 0.6.5 comes out, 0.6 will be free.
Mega has a 5 gb limit so you shouldn't have any problems, however the 500 version is the pc version playable on pc the android version instead requires joyplay,
If you want you can go to my patreon in the info you can find other links where you can download the android version from other mirrors, here unfortunately I can only put one and mega is the best.