They are using very little if any of the phones resources, in the event the memory gets low enough to affect the phones performance then the operating system will shut down what needs to be closed. If you close them manually many may reopen, which will actually use more resources than leaving them alone.
If it bothers you to see them running there are "task killers" in the Play Store that will automatically shut down running apps, but again, many may restart on their own, and you may actually see a decrease in battery life, I doubt performance is going to be affected at all, regardless of what you do, your phone is plenty powerful.
Lastly, if the app is showing as running, when you do open it, it will be quicker to respond.
Enjoy your new phone.