1. How do we expand the map size in the editor? I can see in game the map goes on for miles but you see a tiny square of it in the editor
2. How do you add terrain textures? There are currently only the Yavin ones as I can see. I want sand and some others for the map I'm making
3. How do we add model 'props' e.g trees?

I may update with more but I'm actually trying to make a mod for a game myself for once instead of begging others so help would be appreciated, as there are very few tutorials out there showing these things. Any help appreciated

I don't know about all of your questions, because I am rather new myself, but to add an object (as per your third question) I can help you with.

1. Open Zero Editor

2. Open your world file

3. Select the modes to edit
Picture linked:
https://drive.google.com/file/d/0B0QK5G ... sp=sharing

4. Select the layer you want to add the object to
Picture linked:
https://drive.google.com/open?id=0B0QK5 ... WFLQ2VMVjg

5. Go into "object mode"
Picture linked:
https://drive.google.com/open?id=0B0QK5 ... VREak1LX2s

6. Click place
Picture linked:
https://drive.google.com/open?id=0B0QK5 ... kNxWFdKdXc

7. Browse for the odf file that you want to add
Picture linked:
https://drive.google.com/open?id=0B0QK5 ... WpndEpZUk0

8. Place your objects and save!
Picture linked:
https://drive.google.com/open?id=0B0QK5 ... HBuZnRaRnM