GIMP :: How To Convert Black Dotted Lines Of Paths Tools Into Straight Black Lines

Total buffoon when it comes to getting GIMP to do what I want to do. I'm just practicing with making maps, black lines on a white background, and I've run into some issues I'm wondering if I can get rectified.

1) For whatever reason, the line weight of everything has shifted throughout the file, ending with some lines lighter and grayer than others. Is there a way I can get GIMP to trace all the lines in a uniform black, with uniform thickness?

2) I have tried locking the white background, but often when I select and move my black lines, if I don't click in just the right spot it moves the white background instead, which is really, reeeaaaly aggravating. How Do I get that background to be completely untouchable?

3) In trying to colour the image, I've run into problems with their being a white outline between the colour and the black lines. I think I need to sharpen the image or somesuch? How can one correct this issue?

4) Is there anyway to convert the black dotted lines of the paths tools into straight black lines, in regards to an older file? If not, is there an easy way to trace them?

5) I find the scale too tends to make my image too jagged. I want to take a section of my map, move it too another file and enlarge it to do detail work - what's the best way to do this in order to have a clear image?

6) Any way to translate an image from a MErcator Projection ot a Winkell-Trippel projection, one that works on a Mac?