I’d suggest using the gensurf plugin to start you with a nice even grid of triangles. You don’t have to use it with a heightmap, you can use fractal with a 0 roughness value to start with a flat terrain.
If you use vertex edit, it is better if you lock the X and Y axis before you move stuff. If you want to move the corner of brushes in X or Y, use edge edit first, and then vertex edit to ensure the vertexes are on the grid in Z
yobiko,
gensurf can handle heightmaps larger than 33x33. It will go up to 128x128 divisions. I’m shocked that easygen doesn’t. Perhaps there is an option somewhere that you missed. Howerver, you should remember that the number of triangles grows rapidly as you increase the size of your bitmaps. Eventually, you start hitting compiler and engine limits, not to mention risking high r_speeds.
The terrain manaul included with the editor tells you a fair bit about the requirements of terrain and using gensurf. Some of it is a bit out of though.