In addition to straightening out your XPath, you will want to change
the variable element to look like this:
<xsl:variable name="beginPage">
  <xsl:value-of select="startPage" />
</xsl:variable>

Then you can insert that value like this:
<fo:page-sequence master-reference="page" initial-page-number="$beginPage">

Probably you meant
<xsl:variable name="beginPage" select="startPage" />

--
Oleg Tkachenko
Multiconn International, Israel