If you look at all my accounts on Stack Exchange network, you will see that my acceptance rate is 100% or very close to that.
As I did with English Language Learners, I am accepting answers after a week or two; the only question on ELL for which I didn't accept an answer is the one that still doesn't have a satisfactory answer. (The only answer has a score of zero, with an up-vote and a down-vote.)
By coincidence, a week is the default time a site is left in private beta phase. IMO, it doesn't make sense to accept an answer before the site doesn't go in public beta, and this is for two reasons.
In private beta, the users who access the site are relatively few; there are few users who can answer the question. Accepting an answer would also cause future users who come with the public beta phase not to bother with those questions with accepted answers; they eventually check the questions without an accepted answer, and see if they can contribute with a better answer.
Statistics about the site are being used when the site is in public beta phase, not when the site is still in private beta. What eventually is being checked is the type of questions being asked, independently from the fact the questions have accepted answers or not. See Italian.SE to remain in private beta for another week.
The most important step now is asking good questions about Italian, and closing those questions that are not a good fit for the site as we want it; then, we also need to decide what type of site we want. In all this, accepted answers are not a problem, yet.
When the site will go in public beta, users should understand what questions we consider on-topic, and which are considered off-topic. This is the most important thing, since a site where users don't understand which question they can ask is destined to fail because it will fail to attract experts. Nobody will like to participate in a site where 25% of the questions are off-topic; that would mean a high noise ratio, which would cover the interesting questions experts want to answer.