I might be wrong but I’m pretty sure you have to start your leave on a Monday so last day has to be a Friday. Obviously unless baby comes! I went off a week before my due date and luckily baby came on his due date because the week I had before he was born felt like forever!
Don't have to start on a Monday - I believe it just makes pay easier? Might be worth a look into Teachers SPL to get yourself some more time /money and you might find you can afford to take a week or two off before x
I’d give the latest possible date that’s reasonable. You can go beyond your due date too (I did by a couple of days). If you decide you need to go sooner, you absolutely can. My school made some serious adjustments for me to make it through the last three weeks of school up to my leaving date, and I was much better off financially, but also my daughter was 10 days overdue, and it would have been a long time waiting otherwise!