It's taking forever to paint custom textures across parts of my land, I was wondering if anybody has some tips to share?

Currently all I have is LOD to show all in the creation kit so i can see around the cells.

Set ugridstoload to as high as your computer can handle (try something like 20-25 first) and zoom way out, then make a new weather that has a very bright sun color and no fog, and turn the sky on while you paint. Make the render window as big as possible as well. Also, use the region generator at first to assign certain textures to different heights/slopes. That's about all it's good for anyway. Beyond that, I don't really have any adivce, the landscaping tools svck. I want to try to make an external program to do texture and vegetation painting eventually.

You can use region editor to deploy huge chunks of landscape textures, instead of an object just throw a land texture in ..

How do you know where you're putting anything in the region editor, it seems I'd have to manually work out the grid coordinates and carefully select each one.

Also where would I find the region generator to assign textures to certain heights? Google doesnt seem to be helping.

Read this - http://cs.elderscrolls.com/index.php/Regions with the region editor open and make a small region to try the different settings. It's quite a good guide. Although it was written for Oblivion (I think), most of the information still applies to the Skyrim region editor.