Exploring Portugal

We are a step closer to our final move now. My husband is already living and working in Lisbon (for the past week) and as soon as I can wrap things up, I will be on the plane! Getting excited now...

One of my millions of thoughts has been: how do we get around and explore the coast and the different areas? Not only to decide where it would be best to live, but also to see the country and what it has to offer.

I understand the transport system is very good (not like in South Africa!) but am wondering what the best way would be? Does anyone have suggestions/recommendations?
How easy is it to rent a car for a day or a weekend - is it as costly and as strict as in SA, with big deposits, credit cards only, etc etc?