Slight modification to what I first sent.
set x to (count of words of thisstuff) / 2
set y to 1
repeat while y is less than (count of words of thisstuff)
set AppleScript's text item delimiters to {" "} -- < added delimiters so the words are separated by spaces in the next line
set thisParaSay to words y through (y + x - 1) of thisstuff as Unicode text
say thisParaSay
set y to y + x
set AppleScript's text item delimiters to {""} -- < reset the delimiter to the default for applescript (nothing)
display dialog "Continue?" giving up after 1 -- < this is the dialog box which will appear and allow you to continue.
-- The "giving up after 1" pauses it for 1 second, then continues. You can remove this clause if you like. To abort, just choose cancel in the dialog.
end repeat