In updating the kookma plugins, I started using the plugin icon ( a TiddlyWiki feature less used). The cost is few kilobytes (less than 1~2 kB).
For example see
What is the best practice to include the plugin icon?
Q1- the type of icon to work on all browsers? I use svg.
Q2- the size of the icon? Is the standard size 22pt?
The pt is less common and I prefer px. I hope in the new update of TiddlyWiki, core icons use px instead of pt.