What details from the registration screen do I need to record for future reference?
You will need to record two pieces of information for future use. Firstly you need to record your e-mail address which would look something like yourname@i12.com or yourname@yourbusiness.i12.com

Secondly, you need to record your password.

If I change location (i.e. if I move house or office or change my telephone number), can I still access the service using the same telephone numbers?
Yes you can. The 0845 non-geographic local access telephone numbers are charged at the same local rate everywhere in the country, and because the numbers are non-geographic, it does not matter where you are in the UK, the number you dials stay the same.