Yes, Australia is a nation-state.
establish its own constitution
Each states needs there own constitution for a few reasons. It is to tell them apart and make them what they are.
Each state in the US has it's own constitution, and it's own supreme court.
Yes, each state has its own individual constitution, but they all comply with the United States constitution.
Yes and Yes. The US Constitution applies to all the states. Each state has its own constitution that applies to that state. The state cannot contradict anything in the US Constitution, but they can add things that they feel are missing, or have more stringent requirements for certain things. And the state's constitution sets up and defines the government that will rule the state.
Could impose its own tariffs
Each state held its own ratifying convention
This would depend entirely on which state is involved. For some states, the legislature and governor can amend the constitution, or the people can amend it with an initiative. Each state has its own process.
Every state has its own constitution.
Warrants for arrest issued in South Australia are only valid within the state because each state and territory in Australia has its own legal system and authorities. As a result, arrest warrants issued by one state may not hold authority in another state due to the jurisdictional boundaries and legal frameworks in place. This is to ensure that legal processes are followed according to the laws of each specific jurisdiction.
Australia is a federation of what we call states. each of these is like a country n its own right with its own constitution and sovereignty. so the states of Australia are its country's when a decision is made in the Federal government the states interests are represented by the senators in the senate.