1. I've not paid attention, but you can install more loaders if you want and more versions. Generally what's included is either the most stable or the most current, whichever is more appropriate.
2. Our softmod guide IS the minimally invasive method. Firmware? What firmware? You're confused in your terminology.
3. They are the most stable versions available; there are some beta versions, but unless you're directed otherwise they shouldn't be installed (for example, a problematic USB 3.0 device may warrant a try at the beta).
4. Some loaders offer a feature to automatically select the best cIOS. 90% of titles work just fine and as intended under cIOS 249. You could always consult this thread.