I haven't played with Tau much, but have played against them.

1. Crisis suits are a good starting point .

2. Tau are a fire force. Meaning that they are not that good in assaults, but they can do much damage with Markerlights and Co-ordinated Fire. However you need to learn to use crossfire as well as that allows dropping save from most opponents.

3 .The airpower is useful. I'd say that Barracudas are needed as Skyray is expensive. Tigersharks allow dropping Gun Drones which is a nice tactical choice. Similar to Orca. However you can do a ground force as well. But I would suggest trying to get some aircraft to stand in for Barracudas.

I have couple of videos of Tau fighting against me, so perhaps check one out for tactical advice and tricks. However in epic you should play a style of play you are comfortable with, so explicit army advice is always a bit tricky.