Thanks for the info! I assumed it was a mixture of those, php would be useful for plugins too I guess?
Basically I was quoted $1200 for a bespoke WP theme for a new project of mine, usually I pay freelancers to do it for me but this time I'd quite like to have a go myself.
I would sometimes be working on it at home and sometimes on my lunch break, therefore would it be better to work on a live installation and password protect it as opposed to a local php environment?