I've been playing a lot with Legions of Iron recently and there are a few things I think that are essential for anyone willing to dive in this game in 2016. This FAQ deals with the major technical issues of the game, for the gameplay I recommend you read the manual and check FAQs.

The soundfix.exe crash.
The easiest way I found to deal with it is to simply download these fixes :
- Legions of Iron : http://www.moddb.com/games/haegemonia/downloads/steam-legions-of-iron-sound-system-and-mp-fix
- Solon's Heritage : http://www.moddb.com/mods/haegemonia-vector-prime/downloads/steam-the-solon-heritage-sound-system-and-mp-fix

These work perfectly with the GOG version, as I was able to get through the whole Legion of Iron campaign without any crash on windows 7.

The hidden techs in the research tree
There are only two ways to deal with this.

1) You have to switch to a lower resolution like 800x600 and restart the game to make sure the techs are visible (you can also blindly click on them if you just switch the resolution and do not restart).

2) The second way and is to select the techs via the research tree (see the pic if you're not sure how to access it, I spent 10 hours without noticing it even existed).