Stop at Negeri Sembilan better. Makes Klang Port, KL and Putrajaya within artillery and/or missile range.
Just checked population statistics of these 3 states - about 6 million in total and roughly 60% Malay. That is 3.6 million.
For a long time after successful invasion, the two sides of Causeway will have to be governed separately. We can keep the Sultan of Johor as titular head of state for lands north of the Causeway and give his family more privileges than they had under Mahathir. No or limited voting rights for former jiu hu kias even if they are Chinese. Encourage PRCs to migrate to these states to make Chinese majority there. We will have to get closer to China anyway.
Recalibrate the army to fight a terrorist war in these states for many years to come. Learn from the Israelis - import more "Mexican" trainers. Clear the forests to make it difficult for guerillas to hide ... ahem I mean develop the place and improve livelihoods.
Induce Sarawak and Sabah to secede. They have been unhappy with the Federal government for many years - all the riches from their natural resources have been diverted to develop the Peninsula, leaving them poor and undeveloped despite having rich natural resources. Then "Abang" will be left with only the remaining Peninsular states, a shadow of its former self.