I think you have made a great decision and I agree to the extent that the computer world can seem like a rip off, having been in it since before PC's were a glimmer in anyone's eye. If you get behind and upgrade or two or three big whooping deal, as long as you are satisfied with your work. If you have clients and they want you do do something you can't, then you can decide if you want to upgrade.

You have the ability to draw, paint and photograph, then the computer is just a tool like a brush or pencil. Use it that way and you will grow. I don't know if you are familar with BJHook (http://www.renderosity.com/mod/gallery/index.php?image_id=2142602 ), I believe he uses all the tools for his creations and does (IMO) a fantastic job.

At any rate Good luck, and god speed!!!