What are the requirements for gdoc(())

The only requirement is your web host supports PHP and allows outgoing interent connections. Almost all web hosts do that so it's likely you are ok to use it. If you are not sure please test it before purchasing pluskit (you can test it by create a simple styled text page, adding a pluskit page and in the styled kit page type

@gdoc((key:ah4jzqpk89pj_13fc583j))

You should see a small document I wrote up (note the document is totally nonsense, don't take it seriously)