Hi @Spinorose,
You haven’t provided much description of your LED driver (in terms of what it is or how it’s expected to operate). If it’s a direct drive module that just uses a PWM duty cycle to determine the proportion of on/off time (as a way of setting LED brightness) then the frequency range is just allowable inputs, in which case the default frequency of any of the outputs is likely fine (since it will be within the region specified in your datasheet screenshot). That said, you may wish to adjust the PWM frequency, or your camera framerate, or apply some kind of notch filtering in the camera if you notice your video is flickering due to a poor match with the lights driving frequency.
Exactly, assuming your LED driver is just directly using the input signal as a switch (rather than trying to interpret it and convert it into something else 
)
Most likely the update failed. It’s possible your Pixhawk is one of the models a problem with the silicon layout, in which case you’ll need to use the Pixhawk1-1M firmware instead of the standard Pixhawk1 one (for ArduPilot firmware >= 4.2).
Note that we haven’t tested that with Sub, so it’s possible there are some expected features missing in current versions. It may be preferable to stay on 4.1 until we’ve managed to look into this more - we’ve recently found this issue is affecting more boards than were initially thought, so we’re intending to do some actual testing of Pixhawk1-1M to make sure it supports the expected standard ArduSub features. At the moment it’s possible it doesn’t work for our Celsius temperature sensor, and may not work for DVLs - I’m unsure about anything else.