I'm going to have to disagree with part of this. Collecting emails is a good strategy when there's a concrete availability date and that date isn't too far off from the present.
I recently had a client who was trying to sell a similar(ish) product. Collected emails for 6+ months. When they announced that their product was available, it took them 3 months to get to 50 orders from nearly 10k emails.
Looking back, keeping the email subs engaged might have helped increase conversion from subscriber -> customer, but It ended up not working out nearly as well as we had hoped.
Don't get me wrong selling and getting real product validation is the best.
But emails are one of the most valuable resource for marketing. You can always email people. But even advertising to the people that liked your page will cost you money and will be competing with tons of information.
