1. Generally not.

2. No, its only confusing the first time. All you have to do is get the folder you download for the mod into the mod folder on your computer. No other steps or file editing is required. Read this when you want to try installing one.

3. Yes, from the main menu in game.

4. Yes, and with Entrenchment/Diplomacy you can have as many mods enabled as you like (though most mods won't work with each other unless designed to do so or if one of the mods is pretty small)

5. Here in the modding forum is always a good place to look. The Wincustomize site advertised in the downloads section of the site is also an option but often the mods are out of date. A list of the main mods can be found here with a little bit of commentary by the website creator.

Further, I advise that the Devs add custom map sharing to Sins of a Solar Empire: Rebellion.

Thanks!

I see a lot of great looking mods. One that made me smile: Volumetric Explosions & Damage Effects ver. 1.2. "In addition to glorious explosions and burning ships, you also get crewmembers doing the ol' 'spacewalk without a suit' when ships go down or get a serious blow." Depending on how taxing it is on my system, that may be a mod I end up leaving turned on all the time.