automatic "Wet skim-mate water change" replenish wet skimmate with new saltwater

I would like to implement an automatic "Wet skim-mate water change" so as to replenish wet skimmate with new saltwater. The idea being to make water changes better value ie removing dirtier old water and as on a little and often basis would be less stressful to tank inhabitants.
I envisage it may work like this?

1. Skimmer pump on a daily timer to avoid RO top up filling whilst Skimmer on done with socket timer
2. RO top up on opposite to above daily timer! (this should stop RO water dilution whilst Skimmer on)
3. Level sensor in cup turns off skim pump when cup full (install level sensor in skim cup & use Programmable Logic to turn skimmer pump off for more than long enough to drain cup see below)
4. AND turns on solenoid to allow gravity drain of skimmer cup
5. AND turns on a doser pump to deliver same amount of new salt water.
6. If new saltwater container becomes empty then STOP skimmer and also ALARM

My questions are:
Has anyone done this?
Is my idea sound?
Any problems foreseen with this idea?
What Programmable Logic code should I use for items 3 4 5 6 as not very experienced in programming?