What to do with Shining Coins

Firing your gun while using a two-handed trick weapon isn't typically possible, but there is at least one weapon that allows you to do this:

The Rifle Spear has a built-in gun function while in its two-handed mode. I believe that you shoot it just like a regular gun, with L2. The item description includes the line "it is the only trick weapon with an attached gun," so it's possible that it's the only weapon in the game that can do such a thing.

There are also a number of trick weapons that still only require one hand even in their transformed mode, such as the Saw Cleaver, Saw Spear, and Threaded Cane.

There is a limit of 10 notes that you can have active at any time. Once you reach the limit, older notes are overwritten (presumably in order of writing).

It's worth it to save good notes that provide you with a lot of Fair ratings, so they'll continue to provide healing bonuses.

See also: Reddit