There is no guarantee of getting a 12 month Visitor Visa in fact it can be refused if you give information that leads to being considered a Genuine Temporary Entrant.
Visitor Visas can only be granted for certain reasons, even if approved can have a No Further Stay condition - that wrecks your plan.
The Immigration Department is also trying to make changes to have sponsors pre approved - they tried to get this passed last year but deferred it to this year.
There is zero risk of applying for another visa to be in Australia after a PMV or 309 application affecting that application.
For a PMV or 309 grant you only need to go offshore - we were in Darwin and went to Vietnam for a week not to Ukraine where PMV application started.