Welcome tot he Guild Lotor! GIMP is a good choice; it's free and fairly powerful. As to where to go from here, I'd recommend spending some time getting to know the tutorials section - there is quite a bit of material there to help you get your bearings. Next, when you are ready to begin, post up a WIP thread and ask for feedback. This will encourage more experienced Guild members to offer constructive criticism that will enable you to learn more tips and tricks. Best of wishes on your quest.