First answer: You don't need to unsubscribe, just turn off the notification. Go to your control panel (User CP on the menu bar), click the "List Subscriptions" on the left, click the "Notification" box at the top of the list, go to the drop-down box at the bottom and select "No e-mail notification".
That'll take care of the ones you've subscribed to so far.
THEN you go to "Edit Options" under the "Settings and Options" heading. About the middle of the page, there's a block called "Default Thread Subscription Mode". Change that setting and you should be all set!
Second answer: Further down that same page is the "Thread Display Mode" where you can change the newest/oldest display.
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