@damidgaf If it's a true 5.5W laser the Mana board will be damaged due to the current required, you need to connect power directly to avoid damage.
Maximum power is 255 with my firmware and parameters, but it depends on your Grbl parameters. If you are using the Eleks firmware then yes laser max would be 1000. The PWM output on the Nano is 8-bit, so the range is 0-255. Using 1000 requires the firmware to downscale the output which can cause banding in grey scale images, which is why I recommend 255.
Display Grbl parameters in the Machine menu and check the $30 value, that's the firmware laser max and needs to match the T2Laser value for laser max to achieve best results.