Technically, I have ~10 ongoing comics. ^^; But only two of them receive regular updates; the rest are either on hiatus (whether I want to admit it or not) or comedy strips that just update whenever I have a new idea. All that is to say, I know what it's like to have more ideas than I can handle.
If you like this new idea of yours, I'd advise you to try it out. Do character sketches, write a few chapters, maybe even make a test page or two. If you find yourself loving it more and more as you go, then you can give serious thought to incorporating it into your schedule.
But (and this does happen), if you run out of motivation pretty early on, or hit a wall with the writing that you didn't think about before, take the opportunity to let the comic go, or at least put it down for a nap. This is actually a good thing; it means that you don't have to give it any attention right away. You've formulated the idea and gotten it down, so you can come back to it in a year or two, or whenever you find yourself with some free time.