Starting a new army is always fun. Go team!
Unfortunately, Tome is dead-on in his assessment. Tau are possibly the weakest army in the game, and, the main reason for that is that they actually don't kill Marines well. And that's where I think you're going to find a problem.
If you really, really, really don't want to play a Power Armoured army (and I don't blame you), I strongly urge you to consider playing Dark Eldar or Eldar. However, since you're set on Tau, you probably want a shooting army so regular Eldar are better for that.
One of the guys at the club plays Tau almost exclusively. I'm not sure why. He loves them. He can't afford a second army. He wants to play the worst army in the game for a challenge. I really don't know. But, he is one of the rarer breed of person where losing - continuously - doesn't really bother him. Now, I know most people think they never win, and usually it's really something like one win out of every five games. But going 0-30 (let's say you play two games a week for the active player, you can rack this up in two-to-four months) generally kills people's interest in the hobby and the primary reason Tau players quit the hobby or start a new army almost immediately.
I don't want you to not play Tau. Not even, bro. I just want you to be aware that there's a good chance of losing and "Take to the local GW/Hobby Shop, and kick some Power armored butts" may or may not be a realistic expectation. Check your meta-game, it never hurts. I wouldn't be surprised if your Blackshirt (you mentioned GW so I assume you go there) actually points you away from Tau to Eldar.
Tau rule in the casual metagame, which is generally all-Infantry and maybe one or two tanks in an entire army, and some of them might be Transports. But, if people are even halfway competitive with proper tanks and as many Transports on the board as they can manage, Tau are in trouble.
Pretty much. If exactly this doesn't appeal to you, don't play Tau.A standard Tau list (Read: the only remotely competitive thing we can manage) is:
- A cheap Crisis Commander with Shield Drones.
- As many Crisis teams as you can manage. These are your main killing power.
- A minimum sized unit of Fire Warriors to hide away in the Pathfinders' Devilfish (and only because they're mandatory).
- A good number of Kroot to claim objectives and bubble-wrap things.
- At least one Pathfinder squad. Six strong, no upgrades, only a Disruption Pod on the Devilfish.
- (OPTIONAL) A cheap unit of Piranhas, some with Fusion Blasters, to block enemy movement.
- 1 to 2 Hammerheads. They bring a Railgun on a durable and mobile tank chassis as well as the ability to drop a nice pie plate on hordes.
- Broadsides in any HS slot not filled with a Hammerhead. They bring more Railguns per point than Hammerheads, but lack the mobility and pie plate. Generally, you want a mix of the two. Shield Drones add durability (use them to take Instant Death wounds).
i.e; Spam Crisis Suits. Ignore Fire Warriors. Grab some extra Kroot whenever you have spare points. However, this is good because Kroot aren't anything like painting Space Marines.
Nobody knows. Don't base your army on what might happen at least 8 months from now.