Service Center and donation forms used in previous fundraising campaigns

As we are preparing to enable the Service Center for our sustaining donors, we are running into some questions about our previous donation forms and how to configure future ones.

During the Convio Go! program, separate donation forms and groups were created for each fundraising email campaign.  These forms had both options (one-time donations and sustaing giving) and were only used for those particular campaigns which ran at the most a month.  We also now have two standard forms that are used outside of the campaigns, one specifically for one-time donations and the other for sustain giving.

Part 1 - Questions:

Since some of our current sustaining donors used those donation forms used during the campaigns, does this mean we will have to turn on the Service Center for each one so that they can maintain their account?  Is there a way to turn it on for all of them at the same time?

Part 2 - Questions:

What are the recommendations on how to handle future campaigns?  Is it truly necessary to create a new donation form/groups for each campaign?  Is this the only way to do it for reporting purposes?

Since these campaign forms are only used for a short period of time, will we encounter a problem in the following example?

EXAMPLE: During campaign user signs up as sustaining donor, 6 months later they want to change the date on which their card is charged, since the only way to do this is to cancel the current sustaing giving and enter a new one on the preferred date - when the new one is entered, the current donation form (different from the one used during the campaign) is used.  Will this cause any confusion with the system or might we encounter any reporting problems?

Thanks.