From my own experience I'd say that cosplaying in Sweden is rather easy.
My tip for starting is to either make a easy cosplay by your own or buy one (From what I know if you're about to be in a competition with your cosplay you need to make it by yourself in Sweden, I don't know if that goes for all conventions)
I don't know how many there are, but I guess there are a few here and there.
I think it's only individuals who runs these, and those I've been at are the among the small one, and there's about 300-400 people on those, much much more on the big one like Närcon etc etc.
People do all kinds of stuff, even I don't know the half of it :P
You should come to Kodachikun this october the 5:th (I'm linking to the eventpage on Facebook: https://www.facebook.com/events/1416925518527345/
I think it would be a nice start, get to know some people and take it all from there