Newbie asking a question about GIMP:

Should I place terrain features on their own Layer, or can I draw on the Ground Layer without severely limiting myself in the future? I am working with a 3,000 x 3,000 world map. By itself it functions fine, and I can add another Layer when I am working without problem. However, when I get up to 3 Layers, and more, my PC slows down considerably. So, to Layer or not to Layer? If I can work on one Layer for the terrain, rivers, and lakes without screwing the pooch I would prefer to do it that way. Does anyone have any insight into this situation? Have any regrets regarding a similar situation?

I don't want to find out that I have to do work all over again because I didn't Layer the project properly. Any help with my dilemma would be greatly appreciated.

EDIT: I wasn't sure in which Forum to place this Thread so I ran home to mama.