There are a few things to remember with low voltage lighting.
1) Just because it's low voltage does not mean that you can use thinner wires. Ensure that the wires that you are using are of a sufficient gauge to carry the load at the voltage you are using i.e. 12V or 24V.
You will actually need heftier cables for high wattage lights at low voltage.
2) Voltage drop can be a big issue over longer runs at low voltage
This tool is handy for calculating what you need :
http://www.tlc-direct.co.uk/Technical/Lighting/VoltageDrop.html
3) Ensure that you have sufficient clearance behind the fitting and that there is no attic insulation around it. These fittings can run very hot.
4) Site the transformers somewhere where they can cool down and run safely. I put mine in the attic sitting on large ceramic tiles to ensure they are able to dissipate heat easily.
5) Remember that some LV systems can be dimmed, others can't. You'll need to talk to your lighting supplier about this.
If you want to save energy, consider 230V LEDs bulbs, they are a bit pricy for good ones, but they do provide reasonable light, but still no where near as bright as halogens.