Yes. This requirement calls for being able to provide one or more triple patterns. This is done in one of two ways: through a triple constructor mechanism (example here),
as well as via a built-in triples() function (example here).
Yes (I think), but it depends on your definition. XsRQL doesn't return variable bindings per se. What it does do (as one way in which results are returned) is to return all values satisfying a path-language-specified wildcard. The wildcard is an implied variable. As a simple example, see the wildcarded query here, and its resultset here.
Libby's optional mailbox example shows how to do this with an IF statement, a union query does this, and at the "permissive" end of the specturm, partial and full wildcards fullfill this as well (ie, show me *everything*, or show me everything that's in the foaf namespace).
Not spec'd out in the proposal. I would see this being done by adding a new "resultLimit" declaration to the existing query prolog section. For example: