The 30 day trial is the whole program. I don't know how they control the time limit.
Carrara has many, many, many features and so takes a little longer to learn than, say, Poser. From the start, the render engine makes even minimal scenes look like great art work.
Carrara uses as much memory as poser, but it does not have the memory leaks that poser has. Where poser crashes at least once a day, I have had only one carrara crash in a year.
It depends on your computer RAM, but carrara is very friendly to other programs being open at the same time.  I sometimes have carrara and photoshop both open at once.