Kshitij, to reply to your questions in order:
The output in the online MaxDiff Analyzer shows 95% confidence intervals, both in small numbers (in parentheses) when you look at the results in table mode, or graphically, if you request it, if you request it in the bar charts. A quick and dirty test is that If two items' 95% confidence intervals don't overlap, then they're significantly different. You could also be more technical, inter from the confidence interval what the standard errors are, then use a formula for a dependent t-test, and while that's a little more accurate, it's also a good bit more work.
It does make sense to wonder if items' scores are significantly different.
Of course the sample size does matter (that's taken into account already in the 95% confidence intervals, and you'll need to take it into account if you use the t-test formula).
You can compare confidence intervals in Analyzer, or run tests yourself outside of it. Formulas for dependent t-tests are available in any introductory stat book.