Coming back briefly to supply work- if you are Manchester based you will have Manchester, Stockport, Oldham, Rochdale, Bury, Trafford and Tameside LEAs all within your radius - depending on how far you are prepared to travel (bearing in mind petrol/wear and tear on car will come out of whatever money you make).
You can sign on directly to the LEA pools and to as many supply agencies as you like - but unless you are attempting to get all your work with one agency (this is my main employer box) you do have to be careful re tax.
You will need to submit a tax return and possibly take a tax hit upfront if working with multiple agencies and get money back at end of year (if you want to avoid the opposite where each agency has you as a main employee then you face a tax bill later).
Bear in mind:
The agency is out to make money on you and will try and do the following unless you are firm about what you want:
Get you for the minimum amount per day - which they will then be inflating for the schools to make their profit
Get you in a school for the longest period of time - for which they continue to charge school per day or charge for a finders' fee
Get you as a newbie to travel the farthest
just to get the placement
Get you as a newbie to work in the most stressful schools
as you don't know any better
A lot of schools as I said have permanent cut price supply cover supervisors in place so this means the agencies are more competitive/cut throat
A lot of schools you are covering for therefore is stress-related illness i.e. burnt out teachers or long-term absence i.e. illness whereby the kids have had a succession of short term staff and buggering about
Or a vacancy they cannot fill ask yourself why
Or they have an Ofsted inspection 
It is a great experience to find out just how good you are, strong you are, how inventive you can be...if times have changed while I have been away please let me know but often you might find you have to think on your feet and think fast before being heckled or told 'they did that last week etc'
Many kids will happily write off supply before you've opened your mouth
especially disaffected pupils because of long-term staff absence.
You will need to know as soon as you walk through the door:
The names of the five heads of year or equivalent (To namedrop)
The on-call policy/hod support and how it relates to supply
The usual - stand up at start,coats off, bags on floor, logbooks out etc for you to record or threaten to record poor behaviour
Copies of pupil lists or access to sims - else the piece of paper you send round will have Ben Dover Theresa Green Hugh Jarse etcetera
Have spare equipment with you but ensure you get it back
Have some kind of plan B (even if how many words can you get out of
longer word) while waiting for work to arrive if it has been set
Not trying to put you off honestly. But it can be a baptism of fire and although you leave it all behind at 3.30, keep your own spreadsheet of where you will go etc, it can be very stressful if you actually want to deliver something if you are happy letting them kill each other and make paper planes then it is probably entirely stress-free but then you perpetuate the supply myth/stereotype and you won't get asked back.
When I first started doing supply a decade ago I was on 85 pounds a day - when I threatened to go to another agency - suddenly this was upped to 100 pounds a day. My best was 125 pounds a day and this was ten years ago but it was before the advent of using non-qualified, hltas, LCS etc
i.e. when the supply agencies had schools by the short and curlies and the supply costs were a huge proportion of the budget.
No idea what you would get now - would be interested if a supply came on and told me - but although sums sounded astronomical back then the lack of work at starts of terms and in summer, petrol, car wear and tear and then the unpaid holidays meant you were still working at half rate (but fine if you didn't need all the days iyswim)
If doing a longer stint i.e. a maternity cover I would always be looking in the locals or the TES as opposed to via an agency but often an agency will get you the placement as an introduction so you are then stuck unless the school agrees the finders' fee instead (better to have school contract than agency as is cheaper for school and you can continue to pay into your pension)
Forgot to mention pensions - BIG plus for you staying in the profession but switching school is your pension/pension rights unless you were entirely screwed over
My teachers' pension is frozen and my local govt tiny one as a 'supervisor' not great - now also frozen. So whatever you choose to do in the future needs to take this into account too.
Good luck in whatever you decide x