Custom UI development within SDK for Cloud for Customer

Hi All

I am relatively new to Cloud for Customer and have a few general questions about development within the SDK that I was hoping someone could help me with.

Does the SDK allow you to develop completely custom UIs within the system or are there limitations/restrictions?

Can the UIs for example use javascript, iFrames etc?

Within a custom UI / page can I query 3rd party web services / APIs?

I've found resource videos that touch on the topic but nothing concrete so far, so any help would be much appreciated.

Thanks

Matt