Moving swiftly to point 2...

I know what you mean about the Gaesatae. In an open field battle they can be overcome quite easily by breaking their morale with javelins and surrounding etc. I haven't had much of a problem with them like that yet.

However, you try taking them on in a seige... it's a very different affair. If they are guarding the gates/breech then expect heavy losses. If they are guarding the town square - expect a massacre.

To be honest though, I haven't encountered them in large enough numbers for them to cause me much of a headache.