Yes, you can switch over to annual after your first 5 year hitch is up. Remember, though, that autorenew will renew you for 5 years unless you change your plan, which I think you should only do in your final year. You can also just remove your credit card from your account, which won't actually change your autorenew settings but which will actually prevent the renewal from occurring, if that distinction makes sense. In such a case, your account would be temporarily disabled until you changed your plan and made payment.
Yes, they do exist but since these are one-use invitations, you're unlikely to find them posted on an open forum. You'll probably have to PM a member or ask that a member PM you to arrange for an invitation.
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