Parksavers seem to be the cheapest place currently to get tickets because they have a 3 day free ticket but with that ... It might not last past 2016.
Undercover Tourist is also a thrid party ticket agent that offers tickets with a savings.
As for magic bands... they are not required for a trip. When you stay onsite you receive magic bands because they are the "key" for your hotel room. You can purchase bands but you don't need to. Your tickets will be a plastic card and you can scan that to get into the park and for Fastpasses. You pick your 3 fastpasses (30 days in advance for offsite guest) on the My Disney Experience website. You can get additional ones via the app while in the park after your use your 3.
There is a great thread all about FP and
MDE. I would encourage you to go read it because it will answer a lot of your questions.
Have a great trip!