That half day shared PPA will be your saving grace.
I have done job share with and without shared PPA, and that time together 'in the building' is SO helpful.
If you can divide up subjects, to minimise handovers 'mid flight', then that is also really helpful - so 'I do RE, you do ICT, I do Science, you do History'. It isn't always possible to divide up e.g. reading / writing / arithmetic / reasoning, especially if it is a multi-class year group, as you may be expected to keep in line with the rest of the year group, but if you can, then that is even more helpful.
Having an expectation that all handed over books are marked should be a given, but probably worth spelling out!
Being open to spending your own time communicating - a long telephone call, or an e-mail with a follow up call if needed - is great. This is particularly important if you do the beginning of the week + ppa - remember that you could hand over during ppa, but your partner can't, so being prepared to give up your time at the weekend or end of Friday for their handover to you is vital.
Things like displays, assessments, reports etc need a bit of negotiation to make sure everything is shared fairly. You may find that a routine of both giving a bit of 'your own' time during each half termly break to get all displays set up minimises resentment, and e.g. being sensitive to whether all longer pieces of writing with lots of marking happen in the second part of the week so you may need to jiggle plans every now and again.
If it works, it's brilliant. If one person is always 'giving' and one always 'sticking to their own rigid boundaries' it's a nightmare.