There's nothing to check, actually. Just set up a product that has a price and a name and you can sell that and use its buyer group for an update for any other product later. :)
With pre-orders you can even go back and upload a file to the same product once the file is ready, if you wish to continue selling it later for immediate delivery, or you can just take it off your site once it has served its purpose. You can also just delete that pre-order product after you've done the update too.
Regarding buyer groups, note that depending on your payment method buyers may need to specifically opt-in to be added to the group list. If you are using PayPal Payments Standard this will happen automatically and everyone will be included in the list.
However, free checkouts and other checkout methods (such as the credit card page offered for PayPal Payments Pro/Advanced) will require an opt-in. If you are using anything other than PayPal Payments Standard be sure to advise your buyers to check the box which agrees to receive further updates or newsletters so that you can be sure they are included when you send out your update.