Wow, amazing work! In played and finished portal a year or two ago, and it still stands out as one of my most favorite games EVER. I was a little bit portal-obsessed for a while there I just wish I could draw (or whatever the term for making digital art is) like you!
Hmm I wouldn't go that far. The composition seems similar but different enough and someone still worked their ass of with it so I would not call that stealing. Unless you're talking about some picture other than the card I saw...
When I got to this part of the game I tried to make a run for it, but there was an invisible wall so I tried to back away as far as I can but then i suddenly teleported under GLaDOS claw then yelled "curse you GLaDOS!!!"
That's flattering, but I'm not sure if I can sell prints of the characters that are intellectual property of Valve. Even if it were legal, I'd still have misgivings about it. Maybe you'd like prints of some of my other works?