Are these solid gold or gold plated?

They are described as solid 14k yellow gold throughout, not plated or gold filled. That means the color is the metal itself and will not wear off to a base layer.

How big is 30mm in practice?

30mm is about 1.2 inches across, roughly the width of a quarter plus a little. That reads as a medium hoop: noticeable but not oversized.

Are they heavy enough to stretch a piercing?

Solid gold at this size carries real weight, more than hollow-tube hoops. Most people find 30mm solid hoops fine for daily wear, but very thin or newly pierced lobes may feel the pull.

The pair of hoops is the product; no stones, charms or extra backs are described. Check the listing for whether a jewelry pouch or box is included if you plan to give them.

Can I wear them every day, including in the shower?

Solid 14k gold tolerates water and daily wear better than plated metals, so showering is not a problem for the gold itself. Dry them after swimming in chlorinated or salt water to keep them bright.