I have 4"good" recorders that I use. Gill soprano and alto, an Angel (the heavy one, sold at Colonial Williamsburg or the like)soprano and a Horner(? about $15) sold at most smaller music stores. These are the best sounding ones I own. The alto works well in a smaller church/room setting as it's not too shrill. The only problem is transposing the music for it or capo-ing the guitar up enough to compensate. The sopranos are good for larger churches/halls/outdoors as they are a touch more shrill. I also own a wooden sopranino which I rarely play because it's shrill and I have large fingers.

As far as the link about playing Celtic music on the recorder...go for it. I play it all the time because I have a really hard time playing the pennywhistle ("it's NOT a recorder, it's NOT a recorder!"). I just "flap" the holes to give it that trilling thing that pennywhistlers do that makes them sound so neat. Just listen to the other musicians or you'll overpower them.