If Janome has not made longarms before, I would go with something else. I know Bernina had issues getting into longarms; they made some mistakes that already-established longarm manufacturers did not. Longarms are really different from domestic machines. There is a lot less risk purchasing a longarm that has been around long enough to get lots of user reviews.
To avoid buyer's remorse on a longarm, it is generally recommended to spend a year researching and trying out a wide variety of machines to figure out what you like best in your price range. You can lose a lot of money trying to resell a longarm that you end up not liking.
You might want to join the homequiltingsystems group on groups.yahoo.com for advice. This group is not as active as it used to be, but it's still pretty good.