Facebook character counter
63,206 characters, and nobody should use them
The ceiling is effectively infinite. The real limit is the fold, which arrives after about 480 characters on desktop and far sooner on a phone.
Long posts lose the link preview to scrolling
The preview card sits under the text. Every extra paragraph pushes the thing you want clicked further down the screen.
Echoia does the rest: publishing to ten networks, every comment and message in one inbox. Free for three accounts.