Hi
I'll try to answer some of these..
Job really is that easy... just plug and play. What can take a little longer is just keeping all the wires neat and tied up. This is really important on a bike so not to get in the way of moving parts such as steering.
The problem is with main beam is it is often used for short periods of time (and just a second with the 'pass' button). This means the bulb cannot warm up fully shortening the life of it by a long way... also the 1-2 seconds it takes to light is not the instant light you require on a high beam. With BiXenon this is not a problem as the bulb often moves within a shutter to alter the beam pattern, but often bikes have two bulbs, one for low beam and one for main.
Though HID consumes less power than stock halogen once running (at 35W), the startup current to start the arc up within the bulb is greater than stock. On a bike where two HIDs are being started this load is oten too much for the stock electrics and will often result in one or both lights failing to fire up. There is no simple or elegant way around this problem.
The Ballast like you say can just stick on, but I would be tempted to fix it a little better with ties / and or a bolt of some kind (when installing them myself I often remove a bodywork bolt fixing and sandwich the Ballast inbetween)
I hope the above helps a little, but please don't hesitate in getting back if you need more info
Regards