Ok so ill it clear up for you about what I said about the requirements:
*my mic just broke so a twitter account is needed for communication
You should however still be able to communicate though Skype. Twitter is a odd way to communicate even emailing is better as even one has a email account what I am saying is you are limiting your artist to people who use twitter its not a big thing but its a limitation. So that just a helpful tip
*the art files need to be able to import in to gamemaker (I cant find a better 2D software, plus its what I learned the most)
If you are willing to take any file then that is a problem the only file your artist should be sending you is a png. If they are to send a jpeg you will get unwanted pixels and a white back ground.
You not having a portfolio means two things you are lazy and have not uploaded it so people can look at your work or you dont have the experience to create high quality work yet. Either way those are not very good traits
(I understand files can get corrupted however why not create a portfolio before then or you should of started creating the code so you can have a engine to show the artist)Just a small thing but you also displayed your gif like this
http://pixelation.org/Smileys/snake/laugh.gifinstead of this

Overall you might say im very picky how ever if you want a good artist they will be as picky as I was in fact i would be worry if there where not.
One more thing if you state you age or years of programming experience then you are much more likely to get a good artist.
Hope this helps you understand my criticism.