The seat cover you see is from Cabelas
It used to be a Stearn's and it came from Walmart but they don't carry them anymore. Its pretty much the same cover though. It helps keep your butt happy on the longer rides. Needed? Its nice to have.
Front turn signals (running lights) do stay on when the key is on. Its normal.
Your headlight will stay on with the key. Most states require on-road motorcycles to have a constant on headlight that you cannot turn off. There is a thread on the forum that explains how to grind off a little of the inside of the switch so you can switch from low to high then to off, BUT this is only for the older bikes. Can't remember if there is a way to do it for the newer bikes (like the one you have).
A kick starter is a great idea. Needed? If you have a bad battery of it sits for a long time its nice to have. Check out this thread.
Yes, you can roll start them.
As for the larger pegs I don't know because I don't have any. From what I've heard, most people have to modify theirs by doing a little grinding or clipping a spring.
Stabil or Seafoam isn't needed if you use your gas within a few weeks. I fill up my 5-gallon tank with fuel and add Stabil to it right away. Therefore I have "fresh" gas to use in the bike. Sometimes I add a ounce of Seafoam to my fuel tank, probably once a year. Don't know if it does anything or not, but it makes me feel better.
The turn signals are flexible to a point. They will break. I've laid my bike down hard and they didn't snap off, but I did break the housing (opposite side of the lens).