From: Newark, OH
1). The handles issue is graphics issue and it is impacted by both map size (number of hexes) and then graphic elements (number of counters and map markers).
2). Southern Storm is based on our new Cold War game engine. That is a 64bit code that runs a bit quicker and can handle slightly larger maps and unit counts, but still has some windows limits on object handles. We have done some code changes to hopefully deal with the limit hit in Red Storm.
3). Compatibility. The quick answer there is no. The game engine code has changed, the map files format has changed, and the data structures and number of elements has changed. Unfortunately, that means scenarios and maps need to be rebuilt to meet the new structures. We would have liked to have been compatible, but the shear number of changes to improve the game meant there was no going back. On our end, we are planning after the release of Southern Storm to work on a number of expansions and one will be a reboot of the Red Storm/Germany Reforged content.
4). Modding. Fully supported as before, but with more documentation and a validation tool for data file editing. You will still be able to make scenarios and campaigns. Like Red Storm, map making will still be an external process. We have more detailed documentation,but there should is no push a button map maker and won't be one for the foreseeable future. There will be a new map values editor though. There are other items that can be edited and a few new things I can't talk about right now.
I hope that answers the questions. Let us knock w if you have any more.
Work on Southern Storm continues as we squish bugs and work on features.
Cap'n Darwin aka Jim Snyder
On Target Simulations LLC