Q3 - Can the Plant Booster system be added to an existing garden irrigation system?
Yes, this is one of the strengths of this Plant Booster system.  The Plant Booster system doesn't try to compete with regular irrigation systems, but rather complements them, by handling drip irrigation to container plants in a much more simple, but much better way without the need for timers or electronics of any kind.   While other systems are great for watering the lawn and flower beds, the Plant Booster System comes into its own on decks, patios, and verandahs, where it is beneficial for hanging baskets and container plants to be given only as much water as they need, on demand, whenever they need it.   Overwatering plants on decks causes a lot of mess.  By using a Plant Booster system this can be avoided.
There is no need to discard an existing system.  Most of these systems use 1/4" PVC tubing.  If you already have 1/4" tubing close to where you would like to install you Plant Booster system, then it is a simple matter of using a reducing connector.   It is, however, better to use a dedicated circuit from your existing system with the timer control for that circuit set to 24/7 or “always on”.
If you have no option to link a Plant Booster system onto an existing irrigation system which still gets fed via a timer, it will mean that the Plant Booster system won't give you the very best benefit as it will only control water to the plants while the timer to the circuit it is on. This means that instead of the Plant Boosters being able to manage water supply to the plants 24/7, it will only do it for the short times that the timer is on. Provided the soil in the containers does not dry up between timed waterings, the Plant Booster device will allow water to flow until the set-weight (of each container in their fully watered state) is reached, thus still preventing over watering.