What would be the best time to get there...and the best spot close to bar/toilets/club etc
The best time to get there is around 4 o-clock to get a decent spot, otherwise you'll miss out on a view because of the huge crowd.
Good spots to camp out would be the top of Oxford St at Taylor Square looking west down Oxford St where the parade will come up towards you. The parade starts around 7:45pm and will go for at least 2-3 hours. You can drink on the street (responsibly) without any hassle from police, so you might want to BYO!
There are many bars and clubs around that area, but most will have a mardi-gras cover charge, so be prepared for an expensive night, and also to walk home as catching a cab will be nearly impossible! almost 9 years ago