I have had a couple of stints of supply teaching.
Join agencies - more than one. They'll offer different pay. They don't pay to scale. You can negotiate pay to scale for long term supply roles, usually. You won't get paid through the holidays like you do with regular teaching roles, you accrue holiday pay but it's legal minimum and pittance you claim it back from the agency.
I wouldn't rely on wages from supply teaching, unless I had someone else who could cover all the bills if I didn't get any supply jobs for whatever reason.
Your teachers pension will be on pause while you're on supply as will death in service etc. You will join a generic workplace pension/gov mandated pension scheme through the agency.
Day to day supply - you need to be up and ready to leave the house from about 715am, you may or may not get a call to work.
You have flexibility to decide what days you work / want to work.
The start of term and the end of term are usually quiet for day to day supply.
You get to walk out the building once the kids have gone home and the room is left tidy, usually by 3:45 latest!
Plans may or may not be left for you.
You won't always be respected by children or the school staff.
You will learn a lot and become very adaptable and quick thinking on your feet.
Supply teaching is one of those things I think ALL teachers should experience at some point in their career.