I'm thinking of hiring a developer to design a Wordpress plugin for my site. How much access do you think they would require?
If you are talking about giving him an access to the actual site live, I would say a developer does not need to access a wordpress site to create some general plugin
But if your pluing have something to do with your actual data on the website, he would need an account as editor to be able to test check if the plugin is working well.
An ftp account might be needed to deploy the developed plugin into your website.
but it really depends on what the plugin is doing regarding your content to say if a developed needs to access your website or not.