How do I get costumes, (like a whole tutorial) and do people see my cats on their island?

my understanding was that it's something along the lines of normal, rare, and SUPER rare :) the time/$ associated also makes sense

You get Skein only from buying costumes at random.

You get catnip from quests or exchanging cat items.

How do you get Skein (the blue thread when you try and buy costumes on exchange)

how do i get more catnip!