Hello,
 
1. We do not yet support downloading records from a JMP data table as .csv or .xls, but we have these ideas on a list to consider for future versions.
 
2. When a user downloads a data table from JMP Public, they will get the entire data table.  We do not yet support downloading a subset.
 
These might not have been the answers you were hoping for, but thanks for posting the question in case this clarifies things for other users!
 
PS - As always, we encourage community members to upvote existing wishes on the JMP Wishlist, or add new wishes.  This helps us track which improvements are most needed.  https://community.jmp.com/t5/JMP-Wish-List/idb-p/jmp-wish-list