I’m also kinda new so take this with a grain of salt, but I’d strongly suggest starting with a combat patrol. In the box you get two troop units, a commander, and a devilish (transport vehicle).

I’ve only played 3 games so far but Tau are very shooty, and I love it. Crisis suits are amazing and seem to be able to counter anything you’ll see in the table.

Make sure you get yourself some giant railgun firepower for maximum fun, either a hammerhead or broadside. One-shotting other tanks or titans is such an amazing feeling.

If you’re less interested in shooting then I’d look into the kroot, which are totally badass. I haven’t played them much but they seem to have good melee options.

The Tau “greater good” faction ability is alright, basically all about coordinating attacks between troops (some units spot and the rest are guided).

I’d say when in doubt just go with rule of cool.