i'm in a similar situation..i picked up snowboarding quickly due to having longboarded (skated) for a few years.
on the rental gear, i kept on dragging my toes while carving.
i tried running 25 degrees front, 15 degrees rear, and it helped.
i'd start with something mild like this for your first time with angles.
I wound up diving into it, bought a F2 SpeedCross, just bought some boots off the classifieds here, for a great price, and now i just need to find some bindings..
short version: try 25/15 (or more) on your twintip & softboots to see how you like it.