In a twin rotation speed should not be below Vmc, therefore:
1. A short field take off in a twin is limited by the acceleration to Vmc ( plus safety margin, usually +5kts or even +10kts)
In a single the shortest possible take-off is actually a combination between the soft field T/O technique and the short field T/O technique.
You can't (shouldn't) do this in a twin. It will lead to lift-off below Vmc.
So the ground roll in a twin is affected by:
-weight
-density altitude (if non turbo)
-runway surface ( dirt, gravel, grass or concrete)
-runway slope.
2. YES.
The definition of Vmc under FAR 23 :
".........critical engine suddenly inoperative with the working engine at maximum rated T/O power in T/O configuration (=gear up)"
Flight controls really work based on a very simple principle:
airflow x deflection= effect
Since airflow is speed it means speed x deflection= effect.
Vmc is an aerodynamic control speed.
So at a speed below Vmc you have no (or insufficient) aerodynamic means to maintain control. So you will end up in the trees upside down.
It doesn't even have to be that dramatic, at very low altitude like 20'-30' you don't need a whole lot of bank to get the wingtip to strike and the aircraft will cartwheel. It doesn't need to roll upside down to end up in a heap.
3. I'm sure Flight Safety has a VFR only course, or if not they should be able to adapt the course they have. Simply swap the IFR training flights for extra VFR.
4. Be tempting to fly it with a very experienced ferry pilot.