We are able to apply discount coupons when gifting friends hair, face, clothing, and sets https://imgur.com/a/QDGfeWB
. As for other items, it's best to wait until sales to gift other items such as accessories, instruments, interior items since even purchasing these items for yourself doesn't allow the use of discount coupons.
Gifting beats clothes isn't really that big of a deal as once you and your friends reach at least lv. 6, you can start playing battle parties; such as beat rush battle party (brbp) and that can help you earn a lot of beats quickly (if you or your friends have access to couple garden, gardening is an even better way of earning millions of beats in no time but require bana cash).
To give audition gifts received will probably not happen as people can easily abuse this system. Seeing users with multiple accounts, they can easily collect free audition gifts on multiple accounts and then gift (transfer) the audition gifts over to one account.
I hope this answers all of your questions