If you want it to actually get worn: buy the set, not the statement piece. A matched bra and panty set gets pulled out far more often than the elaborate thing bought for one specific night.
If you are between sizes: size up on anything boned, size down on anything stretch. Corsets and bustiers have no give at all. Mesh and lace have plenty.
If it is a gift: the styling guide is the honest starting point, and a robe or a chemise is far safer than guessing a bra size.
If you want it to cross over to a festival: the strappy and mesh pieces do, the boned ones do not. Rave and dancewear is where that overlap lives.
On care: hand wash, hang dry, keep hooks away from lace. Elastic and machine dryers are why lingerie stops fitting, not the wearing of it.