I have a few more questions relating to questions on the application:
Application Question:
You answered Yes to the question 'Do you hold, or have you ever held, any other nationality or nationalities?' Please provide details.
I am an Australian citizen and hold an AU passport. Is it sufficient for me to state this on the application or do I also need to include a copy of my AU passport?
Yes, state Australian. You will have to enclose your passport in any case to have your visa affixed.
Application Question:
Have you made an application to the Home Office to remain in the UK in the last 10 years?
Does this include the visitor visa that I am currently visiting the UK on?
No, because you didn't have to apply for a visa as such but got a stamp in your passport when being admitted as a visitor.
Application Question:
Have you lived with your sponsor in a relationship like a marriage or civil partnership at any time (including since a wedding or civil partnership ceremony)?
Would I answer yes based on the fact that I will have been visiting my partner / sponsor in the UK for 6 months?
Visiting doesn't usually mean cohabitation, unless you have actually moved in with him and added your name to his tenancy, for example. You are leaving soon to apply for your spouse visa in US or Australia?
Application Question:
Have you or your sponsor ever been married or in a long-term marriage like relationship before?
Does this refer to my sponsor and I having been married to other people in the past?
In regards to previous relationships, I have been married before. Do I need to include a copy of my divorce certificate with the application or is it sufficient to assume that if I am re-married then I was legally divorced beforehand?
Yes it means that and you have to disclose your previous marriage. You will have to enclose your divorce certificate as part of your supporting documents. The fact you have re-married isn't sufficient evidence, as you may have lied to the registrar and told them it was your first. You still enclose your marriage certificate for your present marriage.
Are you marrying in US, Australia, UK or somewhere else? If you marry in UK, did you get marriage visitor visa for it?