Have a look at this:
HQ (175)
Shadowsun 175
Elite (585)
6 Stealth bonded 195 / 6 Stealth bonded 195 / 6 Stealth bonded 195
Troops (400)
6 FW: markerlight 80 / 6 FW: markerlight 80 / 6 FW: markerlight 80 / 6 FW: markerlight 80 / 6 FW: markerlight 80
Fast Attack (255)
Piranha: fusion, 2 seeker missles 85 / Piranha: fusion, 2 seeker missles 85 / Piranha: fusion, 2 seeker missles 85
Heavy Support (590)
Hammerhead railgun/smart missiles/multitracker/target lock 175
Hammerhead railgun/smart missiles/multitracker/target lock 175
Sniper Drone Team 80 Sniper Drone Team 80 Sniper Drone Team 80
Rationale:
HQ: Shadowsun is expensive short ranged an can be targetted while her drones are alive. I like the fluff too but she is difficult to use. Would rather have a tooled up Shas'o here but fluff is nice too.
Elite: I tend to run only one squad of Stealth, and even then with trepidation. There is a reason winning Tau players run fire knife crisis suits...they work ell consisitently.
If your are going to take Stealth in squads of six, bond them. Relying on Stealth as your army center will cause some very difficult matchups for you.
Troops: I have won best overall with Tau at two GT's and also have won several RTT's. OPINION ALERT: Never field Kroot for any other than fluff reasons or you happen to be in love with the models. Compared with the other places you can put your points Kroot are a bad joke. END OPINION ALERT. Also, sread you markerlights out into cheaper, more expendable units. Everyone knows what markerlights can do. The turn a marker unit moves to set up a (or multiple) marks, it will draw fire. Since a successful mark(s) makes your other good units even better and since your good units are harder to acquire, marker units are the first to go if your opponent knows what they are doing. At least make them use up shooting on multiple cheap units and you might even get to fire those seeker missiles.
Fast Attack: I love Piranhas. Hot and cold on the seeker/marker thing. Gun Drone squads can be useful as well.
Heavy Support: Early on your opponent will have two targeting choices Broadsides and Fire warriors. Even with drones the Broadsides go down pretty easy. For your army I think Hammerheads are a better choice. Mobile, survivable, versatile. I personally don't care for the Sniper drones but I believe a skilled player can use them to advantage.