Can you get the apple TV without having to subscribe to Apple TV? So you can just use it to connect to Netflix and other services on ?
Yes, the Apple TV+ subscription is independent from the Apple TV box. Users can have one without the other.
Find apps in the Apple TV App Store - Apple Support
Also, does it have a casting facility on it? I read somewhere that it does but can't find the information now. I wondered if I could use it to cast from my phone or mac book?
Yes, the Apple TV box is an AirPlay receiving device, for local streaming from iPhone, iPad, or Mac.
Use AirPlay to stream video or mirror the screen of your iPhone or iPad - Apple Support
Stream video and audio from Mac with AirPlay - Apple Support
Some apps may have in-app AirPlay controls. Prefer to use that for best experience (stream forwarding). Alternatively, devices can do system-wide AirPlay Screen Mirroring, which would capture the screen and stream that to a destination device. Some mobile apps may blur the lines and switch automatically between the two types of streaming.
The Apple TV box is also capable of audio AirPlay streaming as a sending device, to audio systems that can receive this (e.g. multi-room music over the home network).
