Yes, you'll need both an agent and a solicitor/conveyancer, and you'll need both from the start.
The legal people will need to draw up a Vendors Statement for you (also known as an s.32, and usually takes about a week or so) before the property can be sold. Part of that process will involve a body corporate search, which you may need to pay for in advance. My last one was about $150 from memory. Beyond that, most legals will take their fees out of the sales proceeds at settlement.
Agents are much the same; paid either at settlement or release of deposit. Some may ask for marketing funds in advance but like all things, this should be negotiable.
Good luck with it!
Edit; Oh, and how long is the current lease in place for? You should probably talk to your PM about that and depending on timeframe, work out whether you want to sell with either vacant possession (ie, kick the tenant out) or keep the existing tenant in place. Unless of course, it's already empty.