right, so i've come quite a way since I last posted. Managed to split all the continents up into their own documents and size them properly. Then I set to work using jezelf's tutorial for beginners called 'making maps using photoshop', and have ended up with these two images. First shows all the major rivers (http://img85.imageshack.us/i/swlriverscopyjpeg.jpg/), the second shows topographical info as well (http://img686.imageshack.us/i/swltopographycopy.jpg/). I'm hoping the first (the second is just for reference) could be the basis of my 'proper' map.
I have a few questions - I want all my images to be ready to print in A3, so I've set my PPI to 300, and my image size to the proportions of A3 paper. Is that all I need to do? I havn't touched the pixel dimensions, and I'm not exactly sure what they affect...
I also want the images to be able to be used on the web and as reference in a file on my computer, so when I save them for the web, should I put the PPI and the image size right down?

I'm now going to go about filling in some basic biome regions so I can get an idea of where forests and grasslands and so forth will be, then I would like to work on producing my 'proper' final map with nice terrain and textures and everything else. The thing is i'm not sure which tutorial to follow. I looked at Tears 'Saderan' tutorial and really like the way his map looks, but I'm not sure if it would look good for my continent map, as his tutorial seems to be designed with a world map in mind? I also had a look at a few others but couldn't really decide, and was wondering if you wise folk might be able to recommend me one? Basically I'm going for the more realistic atlas style as opposed to the hand-drawn look.