Ableton is the way to go as hbursk mentioned....the "warping" of waves will be quit the trip and delight to deal with and is a wonderful tool of Ableton.
I am still learning this all myself...Albeton can do some amazing timing functions with its "Warping" abilities. It also can function in ReWire Master and Slave Modes.
I am using a RiffWorks/Albeton/Reason combo as my DAW package right now and love the combinations with the three.
As far as the size of the loop...in Albeton, a whole song can be that.....or not if you choose not to loop...blah blah blah
Good luck on all this and hope we helped ya out on some of this
