I can't answer about mutators as I haven't tried them in RO2, and I haven't made any since working on UT3 a few years ago.
A few quick answers to most of your other questions.
1) Yes that is where RO2 code is, your code should go in <USERDIR>\My Documents\My Games\RedOrchestra2\ROGame\Src
In there you should have a folder for your package, a folder within that called classes, and then within folder go all your .uc files.
2)
nFringe,
UDKEclipse are some IDE's to use, or you can use Notepad++ or a text editor of your choice.
You can use
UnCodeX to very easily index and explore RO2's code base.
3) Create a shortcut to <steam install location>SteamApps\common\red orchestra 2\Binaries\Win64\ROGame.exe and append " make" to the command line. so the command line will look like this:
"C:\Program Files (x86)\Steam\steamapps\common\red orchestra 2\Binaries\Win64\ROGame.exe" make
You will also need to edit ROEditor.ini in <USERDIR>\My Documents\My Games\RedOrchestra2\ROGame
Find the section [ModPackages] and add this line for each package you want to make
ModPackages=PACKAGENAME
6 & 7:
http://udn.epicgames.com/Three/UnrealScriptFunctions.html#TimerFunctions[url]http://udn.epicgames.com/Three/UnrealScriptFunctions.html#TimerFunctions[/URL]