How does Cassius describe the "enterprise of honourable-dangerous consequence" that he and other "noble minded Romans" are to undergo?

You've said it yourself, really. Cassius, particularly as he is trying to persuade Brutus to join him in leading the conspiracy, emphasises the "honourable" before the "dangerous", and tries to paint the whole affair as being a noble, worthy office. Cassius, of course, does not actually describe the murder much beyond the quotes you include. Though when he does, he is at pains to make it seem noble.

Brutus takes up the same theme later in the play, arguing that the conspirators all attack only "the spirit of Caesar / and in the spirit of men there is no blood" - an idealistic, noble thought which is somewhat crushed, when, after murdering Caesar, blood pours out onto the floor.

Brutus has to improvise the hand-washing-in-blood to make the very real blood into another supposedly noble symbol - though, by this stage of the play, there's a definite sense that all of the nobility and idealism has been compromised.