What would they do for the hours after school finished normally or if work on weekends?
Sounds like a work / life balance problem. Companies will have to be made to change their working practices, allow more remote, flexible working hours and reduced time.
UK is, very, slowly starting to move to a 4 day week for work (reduced hours, not cramming in 4 days x 10 hours). The productivity increases along with recruitment make it worthwhile. My company isn't there but 35 hours + 50 days holiday so not far.
That would solve the 4 day school day. Also allow for parents to educate their kids for 1/2 a day if needed.
Yes but not for long.
As (generally climate denying) people love to point out, wind and solar is erratic power generation. For this reason you need triple capacity Vs requirements.
This means that for a huge amount of time you'll have excess energy, once we start to be predominantly renewables, battery storage is expensive. One of the solutions is to create hydrogen, also pumped hydrogen, etc.