Hey there, Welcome to the Greater good!
First off, don't buy those things individually - get the Tau Battleforce box, as its probably cheaper and gives you more varied stuff to get you going.
http://www.games-workshop.com/en-WW/Tau-Empire-Battleforce
Secondly, if you get the Battleforce set, you can definitely make a viable list for casual play / games night. This is what i would do:
HQ
Commander (use a crisis, paint his head white), Dual
MP, Drone Controller, Target Lock, 2 x Marker drones, 152pts
TROOPS
FW x6, 54pts
FW x6, 54pts
ELITES
Crisis x1, Dual Plasma, Vectored Retro Thrusters, Gun Drone x2, 81pts
Crisis x1, Dual
FB, Vectored Retro Thrusters, Gun Drone x2, 81pts
Stealth x3, Counterfire Defence System x3, 106pts
FAST ATTACK
Drone Squad, 4x Marker Drones 56pts (Commander attached here)
Tetra x1 (proxy Piranha, leave wings off when you build it) Disruption Pods, Sensor Spines, 55pts
Now I have gone overboard on the toys, but you could easily take some off to come in under 500 points. Commander provides your marker lights and some missile fire while staying out of range, Fire Warriors give your ObSec and decent rapid fire, solo Crisis suits can deep strike and target Vehicles (Fusion Blaster) and
TEQ/
MEQ/
HQ units (Plasma) and use VRT to get away, while the Tetra provides more marker lights and Line breaker / late game objective grabber.
If you wanted to add to this list, I would suggest one of the following (in no particular order - try play testing with proxies first!): Another Battleforce Box / Broadsides / Hammerhead-Skyray combined box set / another Crisis suit set / Riptide. More fire warriors (or even Kroot) would be helpful but the bare minimum you get from the box should see you straight for a while.
Hope that helps!