i think the key here is to treat every employee individually as they will all have different circumstances and different concerns. Some will be in contact with elderly parents. Others won't want to take crowded public transport. Others will have underlying health conditions, or be in the age bracket that puts them at risk. Others will be carers for people in those categories. Asking individual employees what they feel comfortable is probably the way to go, if you have the resources to maintain that in your office.
Listening to feedback from your staff may give you a better picture of what you need to do. Maybe stagger start and end times. Work shortened hours to avoid public transport and crowded lifts. Maybe have 'team A' in the office for a week and then 'team B', that way, if there is an outbreak, only part of your workforce will be affected.
Social distancing will be important, And protocols for shared common areas, etc.
Advice is available from relevant departments in each state. in Victoria, the suggestion is that if people can work from home, they should continue to do so. I think this may be in effect for some time.