$ 400 is a pretty nice budget to work with Richard
while looking at quality over quantity like you mention
20 mm pentax xw and your barlow gives you 60x/120x
usefull mags for most dso .. running out around the $300 plus range .
10 mm xw for the same dollars takes care of your dso and planetary
120x/240x but leaves low power a little financially challenged for the hundred or so you have left .
pentax xf 8.5 at around the $200 mark is also a great eyepiece
leaving a couple of hundred left .. maybe the
Hyperions and there clones are an option for you to mix things up a little
with any of the above to get a good result to suit your needs .
best wishes with your choices
graham