Yes. Those prices are before tax so you actually save a bit more than $150 when you factor in the 6.5% sales tax.
You can purchase them online using links on the members' website or by phone by calling MS. They will give you a confirmation number that you present at "will call" when you get to WDW. You can opt to have vouchers mailed to you but they charge a shipping fee.
Your year begins when you pick up the actual annual pass.
To have Charter Status, you had to have purchased Annual Passes when they first became available and renewed them every year since. If you move to/from Florida or purchase/sell a DVC Membership, Disney allows you to move between the various Charter classes as long as you continue to renew each year.