You did put a steep learning curve on yourself for the Bigma, but you should do okay. I actually received mine a day or so before the May 5 event at the museum. The biggest thing to get used to is the weight. With the camera, the whole kit weighs in at about 5 pounds. It's not bad for the first few hours, but after a full day of shooting, you will feel it.
One thing you will notice with the new lens is that the zoom ring will feel pretty tight. It was a real chore to turn for the first outing on mine. It does, and will, loosen up with use. So your first outing may result in a sore wrist from turning the zoom ring. It gets better pretty quick though.
I leave the grip/tripod mount on the lens and use it for a secondary strap. I have moved it into several positions and so far have liked it best on the right side of the camera. That way, it's pretty much out of the way, but it acts as a nice carry handle when walking around. Believe me, it will bang your around if you are walking quickly! I did like it one the top, but if you ever use the flash, the grip will block the flash.
One last thing on the sigma, be real careful using the flash. The sun glare shield will get in the way and give you an interesting shadow, even when it is inverted, so take it off if you use the flash. Also, too much zoom will also give you the shadow. That's one that has bit me.
Shoot away and have a blast with it. It will feel heavy for a bit, but you'll get used to it. The balance is pretty good, so if you get a bit of a shake, take your left elbow and rest it against your body for stability, or kneel down in a comfortable position and put your elbow on your knee. Anyting that helps hold the lens steady until you get used to the weight.
Here is an example of flash with zoom, and a couple of me with the Bigma.