don , if you are using gimp as a portable app, be aware that it might be a cut down version, so if you are missing some functionality you might have to get a version from the creators w ww.gimp.org. of course it would be just like any other install to windows
the portable app project ports versions of many linux applications in a portable format that can be kept on the desktop without actually installing in the usual windows way.
the launcher is not neccesary, but it gives you a way to organize, down load and install multiple portable apps. The original idea was to keep all of these apps on a thumb drive that you could use on any windows computer without having to install the apps on each computer. of course they run faster if you keep them in a folder instead of on a thumbdrive
seems like you have got gimp working by itself, which works fine, just a bit of work figuring it out. cool
inkscape might also be useful, and the launcher is an easy to try and remove many of the apps available