Well, islands textures can be created using .paa files. To create your land mass. Use either a DEM, or get a program called terragen (freeware). It'll let you randomly create some nice islands to work with. But remember, you can only have island in OFP. It you create and map and put land every where, then ingame, there will be a verticle drop all around you map that will cause you to fall into the sea.