Struggling in Cats of the Cosmos

I am a new player (two weeks) and therefore do not have many cats. On friday I will get Lone Moon Lunos (on 23A), but I also have the option to get Sirius (on 5A) by using a platinum ticket.

Should Lunos be sufficient, or should I also go for Sirius, for coamos 2-3 and beyond, or would Sirius be a waste of a plat ticket?

I really have to struggle to advance, so it kind of feels like I have hit a wall…