Your overthinking it, it's not that complicated,
If you are going to do paye then set it at 30 hrs ( they can work more if needed ) and you work flexi time set over 6 days
We don't work in bad weather, and have never been more than 2 days behind - always upto date, but we run strict scheduled rounds.
If your concerned take someone on as self employed they give you an invoice for hours worked.
I'd only take on people under 25 if most work was commercial, if you want them to drive then insurance is extremely expensive, if not impossible a good worker is also one with commitments - family, mortgage, rent etc...
Darran