Samsung bundled with a whole load of apps already. There is no such thing as "pure" operating system in the strictest sense of the word. Which variant is your I9505? LTE and AT&T, or somewhere else?
Search XDA forums, or use Samsung's own software to check for the latest if OTA is not available?
Do you have some preconceived notion that "latest" must be better? The bleeding edge is not always good, especially if your current firmware is stable. If you are talking about removing all the Samsung stuff, then firmware is not what you are looking for, but rooting.
The Model M is not for the faint of heart. You either like them or hate them.
Gerbils unite! Fold for UnitedGerbilNation, team 2630.