Anywhere, any time! It's best if you go to Cons though, or cosplay with a group of friends, it makes it more fun.
You can't buy the entire outfits or horns from anywhere.
Try the cosplay suggestorator..
You should cosplay your favourite character from a game or anime or anything in general.
Yes. He is the creator of Homestuck.
Homestuck can be read on mspaintadventures.com
As fo now there is no Homestuck Manga in existence.
Depends on the cosplay. It could be made out of satin, polyester, cotton or many other things.
There should be a cosplay store in the United States, but if worst comes to worst you can just buy cosplay online.
No there isn't one. But you could just find a regular coffee shop and start meeting there in cosplay with your friends. In time, it might become a cosplay cafe :)
No, anime has a very distinctive look that Homestuck does not have, anime also is generally reserved for animation that has come out of Japan or another area of Asia while Homestuck is western. While Homestuck has had influence from anime, it is not in and of itself anime.
Nepeta Leijon's best friend in Homestuck is Gamzee.
Cosplay is short for Costume Play. Although the majority of costumes are of anime and video game characters, it could be a costume for anything. You could dress up as a dog and it would still count as cosplay.