Just to clarify Sunday's are not part of the working week but are classed as rostered overtime - if you are working 12 hour shifts you'll be rostered to work 14 shifts over a 28 day period. So a week including a Sunday would be 4 x 12 hour shifts in total, a week without Sundays 3 x 12 hour shifts.
Overtime can be worked on your rest days as long as you do not work more than 72 hours in a rolling 7 day period. This will be reduced to a maximum of 60 hours in January. So maximum of 5 x 12 hour shifts in a rolling 7 day period. Sundays are paid at 1.5x your hourly rate and other overtime not on a bank holiday at 1.25x your hourly rate. Overtime isn't always guaranteed though and works on a equalisation method so in theory everyone should roughly get offered the same.
Bank holidays - if you are rostered to work you can choose either higher rate or pay (2.5x normal hourly rate) or lower rate of pay (1.5 normal hourly rate and a day to be taken off in lieu). Working a Bank Holiday on your rest day you can add 0.25x your hourly rate on to the method of pay you choose (Don't quote me on that but pretty sure it is that rate). Christmas and New Year are different and are generally agreed each year with the union.
Also as you are only contracted to work 35 hours a week and you will be working 36, you will have an additional rest day on average every 12 weeks - sometimes you are offered to work it depending on relief spare availability and equalisation as mentioned above.
I'm not so sure about the Guide Bridge area other than Guide Bridge itself is controlled by Manchester East Signalling Centre so can't really answer your questions on that front.
Uniform is provided, consists of boots, navy blue cargo pants and NR branded polo shirt/t-shirt plus fleece/gilet. If you want to wear it or not is generally up to you. The only thing to be expected of you is wearing a hi-vis if the walking route instructions require it.
