1000mA should be enough for the most guys here, but is it possible to increase the voltage, for example up to 48 volts?
So each string could give out max 48 watt.
Nope- the CAT4101 driver IC is only rated for 25 volts. That's why there's 6 of them on the board. The nice thing about shorter strings is more control or higher resolution when dimming.