As the private beta is about 'priming' the site with questions, should we accept answers? Or should we wait a while to give public beta users a chance?
Yes, if you ask a question and get a great answer, you can accept it. If you get an even better answer later, you can change the accepted answer.
That having been said, accepting an answer is optional. It's optional now, and it's optional after the beta opens up to the public. So please don't ask people to accept an answer. The system reminds them automatically that they can accept an answer if they want.
Here is a pretty good discussion of this issue:
Should be relevant here, too. The primary concern is that the likelihood of any additional answers is reduced once an accepted answer is displayed. This can be a problem if an early answer is not the best answer, or even in some cases if it is inaccurate or even wrong.
To get the best answers, both to answer your question and for future reference, you want as many answers as possible.
A good reference on StackExchange Meta for accepting an answer is: