You can edit the terrain by manipulating one point at a time, which I have done for small areas before, but never the entire map. I have a couple of maps I have made before with the editor and I'm going to give it a shot and try to make them into Il-2......however if a majority of the map of water, does that simplify things any?
Ive been looking around at other maps and some of the satellite data and I've found some areas that look close to some of the features I'd like to incorporate, only trick would be to get them together in one map and seamlessly together.....more I've thought about it, I may end up doing something along the lines of the Solomon Island chain, just not quite as large....not sure yet....my imagination seems to always do this, start adding on so many details that the hard task becomes a hundred times harder >.>
Having lots of water simplifies things vastly. Nothing as easy to make as islands in a vast surrounding ocean ... you can probably cut down the percentage of pixels that need to be edited to very low numbers, 10-15% of the area ... it all depends on the size of the islands you wish to make.
And of course you can combine islands from anywhere on the globe and create a new map with them, you just paste them onto an rgb 0 background which later becomes water ... you can also splice land areas together, but that needs to be done a bit more carefully in the lines where the spliced areas meet ... if you proceed that way, then either clone or soften/blur or rgb to target brushes become very handy ...
And even better is that a map essentially only needs a 256 rgb b/w/grey image to create from. Once you have that one basic image set up, then you can make map_h / map_t / map_f / map_c ... only the ed_m01 maps needs some fancying up with an overlay of some kind that gives a nice graphical look ... and it's here that splicing land areas becomes somewhat problematic since joining up map overlays may need color adjustments and very careful editing.
Pasting island overlays together on one map on the other hand is a piece of cake ...
I know that Kevin's map tutorial suggests that you make several maps with several elevation types that can later be combined together, but actually you only need to use the Sturmovik grayscale elevation and you're set to go with your basic map.
Also a very handy site to make ed_m01 maps from. This site features several types of overlays that you can use:
http://www.maps-for-free.com/Zoom in on an area and then compare the different overlay types: relief/OSM/map/satellite/terrain ...lots of choice of styles and info ...