<p><strong>A. There's a number of levels of association of similar questions</strong><br>
$\quad $ (4 by my reckoning, if we also count 'not quite similar enough to do anything'):</p>

<ol>
<li><p>Where the questions are exact duplicates, to the extent that they invite identical answers - and both have answers - they should usually be merged (preferably into the better question; if they're of similar quality, merge into the older one). If they don't both have answers, treat as 2.</p></li>
<li><p>Where the questions are asking the same thing - to the extent that answers to one will solve the other question, but the answers themselves don't really <em>answer</em> the other question, one should close as duplicate; again the better/more canonical question should normally survive, though the quality of answers and age are other factors to consider. </p></li>
<li><p>Where the questions come close to asking the same thing, but in a different way -- in a way that invites questions that to some extent explore different aspects of the issue -- then they should probably both stay open, but be linked (both ways) via comments. See <a href="https://stats.meta.stackexchange.com/questions/2511/asking-for-clarification-on-the-benefits-of-redundancy-or-multiple-questions-and/2513#2513">this earlier post</a> for some discussion of that issue (see the Jeff Atwood quote in particular)</p></li>
</ol>

<p><strong>B. I suggest doing it in stages</strong></p>

<ol>
<li><p>I suggest taking care of flagging any you think should merge first. </p></li>
<li><p>Then depending on your privileges, either vote to close as duplicate or flag the ones that should close as duplicate.</p></li>
<li><p>Then link (via a comment in each) any that should still stand separately but where the answers to the other question may still be useful.</p></li>
</ol>

<p>[I'd also suggest that with wholesale flagging, to avoid overwhelming the flag queue -- about half a dozen flags at a time is no problem, but two dozen in a day on the same thing (some people can do that many) might lead to missing a more urgent flag (such as a spam flag). If it's a lot, spread it out a bit. This also has the advantage that if posts do get bumped, the front page isn't full of old questions all on one topic.]</p>
