Yes, opens are ok, but you really should learn to use 4th finger too. Sorry you started out with your hand in the wrong place, but see now how it limits you? Many times using 4th finger is the fasted way to do it, like with grace notes. Sometimes you want to keep the same tone color, usually on slow airs, laments, etc. so you use the 4th finger. The open string has a more ringing tone, and will sustain longer than a fingered 4th. Get crackin' and learn both of them, you will be a more versatile fiddler for your efforts!