Question One: The conditional sort is based on the search:highlight, if
it is decimal, sort the putAmount and then incarnate the document.
Notice: The "Rationale" is that currency and amount must be paired. In
each search:snippet, the currency is one search:highlight while amount
another. I would imagine a pure XSLT conditional sort in below manner.

=====================================================
 B B B  <xsl:param name="sortAmount">
 B B B B B B B  <xsl:for-each select="highlight">
 B B B B B B B B B B B  <xsl:sort select="if (normalize-space() castable as
xs:decimal) then descending
 B B B B B B B B B B B B B B B  else ()"/>
 B B B B B B B  </xsl:for-each>
 B B B  </xsl:param>

 B B B  <xsl:template match="result">
 B B B B B B B  <xsl:variable name="doc" select="document(@uri)"/>
 B B B B B B B  <xsl:element name="Trade">
 B B B B B B B B B B B  <xsl:for-each-group select="." group-by="@uri">

A select="." on for-each-group is an attempt to group a single element
and if the group-by="@uri" selects a single grouping key value I fail to
understand what that whole attempt is about.

Question Two: Below produces the same result by replacing Line 55 - 60
in my original XSLT module. Can someone point out if below module is
syntactically correct? (It runs fine in the Oxygen.)

B B B B B B B <xsl:for-each-group select="." group-by="@uri">

Same here, a single element grouped by its single @uri attribute value
simply processes that single element.
Grouping doesn't make sense on a single element with a single grouping
key, in my understanding.