[Sid Squid]

Assuming the 'main ignition wire' means the connection that will tell the alarm that the ignition is switched on, then yes, the orange from the switch is the one you need. Don't use it as the ignition cut - if you do the whole electrical system's current will pass through the alarm and the switch probably won't be able for the load.
Cutting the green/yellow wire will work as a starter disable, but if you look at the bundle of wires on the outside of the battery box on the right hand side you'll find a two pin connector with a short length of black wire looped back in it, (it's taped up so may not be immediately obvious - I'm guessing this is for a component not fitted to UK bikes, but I've no idea what), cutting the loop disables the starter - you can fit the immobiliser's starter cut switch to the snipped wires, very convenient. (Curvy only, not some non UK bikes).
The next one is a problem, the instructions you've quoted refer to an ignition system the SV doesn't have, some ignition systems switch off by 'earthing' a connection so that current doesn't flow through the system but grounds out, you'll need to arrange the immobiliser switching so that setting the alarm cuts the current to the igniter.
Most alarms have a two way immobiliser switch so that either requirement can be arranged, make to kill/break to kill, check the instructions on yours.