Is this wise?

A couple of weeks ago I started jotting down a couple of ideas for a story.

As with most fantasy writers, my stories take place in a world created especially for them. A whole world demands more than just one story, and I've always planned that my original story be the first in a three-part featuring the same characters.

This new story was set in the same world, but in an entirely different place and with completely different characters. I've so far written just over 7000 words, just to see if the original idea actually works on paper (screen). I think it does. But then I would say that. I have sent said words to my sister for an objective opinion.

Is it wise to start another story before the previous one is completely finished?

On a lighter note, I bought some reduced-price garlic prawns in M&S earlier and am planning a posh stir fry. This can only end in wonderful deliciousness and no food poisoning at all in any way.