Landscape Creation

Hi all

In advance, sorry for the noob questions as I am quite new at this.

Just have a few questions about landscapes and the textures.

With landscapes is it important to keep them uniform eg; 400x400, 1000x 1000, if so can you just add a 400x400 at a later stage. If not can I just add landscape in a direction only wide enough that I would have rock meshes on each side to keep you in, block the view and so on?

2nd can I have more than one landscape over the other one if I want a steep cliff jutting under itself or could that cause issues? Is it best to have one landscape and use meshes to create the whole effect of the cliff and just have the landscape jut up vertically as best it can.

3rd when I alter the landscape that I have made it shows the grid squares of the landscape that I altered and I have to build the lighting on it to have it look ok again. This is fine but I’ve watched a video or 2 of others doing this and it seem much smoother and no lighting issue.

4th the textures don’t seem to work the greatest in blending and general use. If any one knows a nice easy video link to watch as I watched one and well it seems there is some kind of mix up as to what is the right or wrong way (have been told the video is wrong) so I have redone it but still not sure.

5th on the last note for now can you tell me how to get my main map. Keeps loading up my test one then I have to manually pick mine and load it. Minor thing but a pain.

Just like to say thanks to anyone who helps and have a good night