I might be able to help to an extent.
Which theme version are you using?
I can’t save and output custom fields
Do they not save at all or are they not being displayed? Where are they supposed to be displayed?
Note: If it’s a shortcode issue from within the listing then that won’t currently work.
…download link doesn’t work
Could you elaborate on what steps were taken, and where, for the link to be determined not to work?
filters don’t work either.
More than likely same issue as with shortcode usage in listings. Which filters aren’t working?