How to add more icons?
The easiest way to do it is to install one of many 3rd party plugins for that.
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Is plugin X supported?
This theme was built with best WordPress practices in mind, which means that generally any 3rd party plugin should work. But since there are thousands and thousands of plugins in official plugins repository (and other thousands of premium plugins on various marketplaces), it is not possible to make sure if it really does work with every plugin out there.
How to install WordPress?
Please read the official tutorial on WordPress Codex.