Questions regarding Rem 1100 barrels for rookie

My pa let me borrow his 12ga. 1100 and I would like to try my hand at clay shooting. The barrel on it now is not vent. rib. Which I assume means I need to get another barrel if I am going to be shooting more than one clay an hour. I need to get a good barrel for the very green.

Any suggestions from the pro's on what would be a good length, choke, etc... Any other suggestions are welcome... thanks all...

Stephen E. Jordan