The order of your podcasts is by date of the post. Newest listed first and so on.
To re-order the episodes, re-date the posts for best results. You can also turn on the iTunes order tag, but this will only work for iTunes and other podcatchers that use that tag.
To get more episodes into your feed, go to your wordpress settings > reading tab and set the syndication reading setting to 50 or so. Also you can set this in powerpress > feeds tab.
Give iTunes and all other directories a few days to get the change.
-Mike