Each hub is a separate system. Adjusting just the lever does nothing to allow for wear/binding discrepancies across the axle.
Also if you adjust the lever cable first, then you may not be able to correctly adjust the shoes. The operating lever should always be the last adjustment on any such mechanism.
3-5 clicks is the accepted optimum range as it is enough to ensure application but not too much to allow for stretch and future adjustment. The Omega handbrake mechanism is NOT self adjusting.
It still makes me wonder why Vauxhall (and perhaps other manufacturers) did not design the system to automatically adjust the handbrake cable / rear pads together.
Its an ATE system, used by loads of manufacturers at the time, very common for larger cars with rear wheel drive and discs.
The basics are this
The handbrake cable must be adjusted such that there is a little slack with the handbrake released, there should be no tension at the operating lever at the rear of the rear brake backplate and the return spring must return the actuating lever to its end stop. This ensures that the brake actuating lever is set to give complete travel.
The shoes are then setup to match the drums (very slight rub on rotation).
The handbrake cable it self shoudl rarely need any adjustment unless its replaced or has stretched following fitment of new.
Rear shoes should only need adjustment for wear.
The trick has always been to use the handbrake and slightly apply it for a few seconds when driving at low speed every month or so, this keeps the drum faces clean and helps to stop it seizing up.