Have bought a now TV box and find it pretty useless with the apps on it. Want to download Plex but unsure as to wether I need a PC for this, do I need PC plugged in while using Plex or can I do the whole thing through a iPad ?? I don't have a PC
You probably can do, the iPad has a web browser. If you can download the Plex app to the iPad and it will let you unzip it / upload it using the web browser it should work. Read: Install Plex On The NowTV HD Box - Step By Step Guide As you dont have a PC do you have some device like a NAS running the Plex Media Server? if not then Plex will be pretty useless for you unless a friend is sharing their Plex library with you.
I don't have NAS. Would it work with chromecast. Is that the way it would be streamed from device to box/TV ?
Plex works with a Chromecast, however you still need a Plex server to store all your video to use Plex on a Chromecast. The best you can really do with a NowTV Box and no computer is probably installing the Roku app on your phone. The NowTV box is a re-branded Roku and the Roku app will recognise it and let you stream certain media to it from your phone. Here is a link to the Roku iOS app.