New Android User Needs Help

I've been an iPhone user since it came out. However lately I found that whenever I opened my phone I would just swipe back and forth between pages. I was bored with iOS. In the early years it was kind of fun jail breaking my iPhone to get features I wanted (I remember having to jailbreak to get features like folders and the ability to take video). That no longer exists with iOS. Not only is jail breaking a bitch now a days, but for the most part iOS is polished enough to where there's no need. I was willing to make the jump to android, and the Nexus 4 really made that decision easy for me, best value by far, and way ahead of my iPhone on the spec sheet.

The help I need from everyone is with different ROMs and launchers. Forgive me if I'm using the terminology incorrectly, I'm new. The N4 comes with stock android and for the most part everyone spesks so highly of stock android, so should I even bother with different ROMs and or custom launchers and the like? If so any suggestions, and how do I go about it? Is it like jail breaking an iPhone in any way, or does the open source aspect of android mean it is different and hopefully easier?

In all the post your screen shot posts I've seen an array of different, some cool, themes. I call them themes because as an iPhone user I only know of them as how that sort of thing would be referred to in Cydia, maybe I'm wrong in referring to them as that. I'm referring to people phones who had app icons that were all circular or black and white etc. How do I do this? Also, I've seen where in the lock screen circle people have had the lock to the right and the camera to the left. On my phone it just unlocks no matter where I swipe in the circle. How do I add the camera and other apps if possible to the lock screen circle swipe thing?

Any help would be appreciated. Thanks.