About your text, I would always use Inkscape for something like this. I know you're still getting to grips with Gimp and maybe don't want to have to learn something else, but it's quite easy to do. I found a simple tutorial that explains it quite well...
http://goinkscape.com/how-to-curve-text-in-inkscape/
When you've got your text as you want it, you can export a PNG file & open this file in Gimp, then copy it & paste as a new layer into your main image. I do this all the time & it works quite well. Oh, and I usually import a jpg of my main map into Inkscape before I start, then lock that layer & create the text on a layer above. This lets you mess about with sizing and positioning against the base map, so you've got it just right for when you export the PNG. Hide the map layer before you export, so you get a transparent image. (I should probably put up a disclaimer that I'm a huge fan of Inkscape & can't see past it sometimes!
)
Now, having said all that, what you've made so far really doesn't look that bad. Not quite sure about the white background though. Is that just temporary?