mum dying - what do I need to know for afterwards

So can you have a conversation with her? Does she know what the situation is? Because the easiest thing in terms of what happens after she goes is if she's told you about all accounts and anything else you need to know. But I appreciate this may not be possible for a range of reasons.

There is a government website/page What To Do When Someone Dies, which you would probably find it helpful to read.

Do you know her wishes re funeral?

Re how long this stage may last, you should be able to ask her nurses or doctor, they should answer any questions you have.

I'm sorry to hear this. Are the palliative care team involved at hospital? They should be able to answer more of your questions in your mother's case. I'm a speech therapist with a special interest in palliative care but I still wouldn't be able to tell you how long I'm afraid. It might be sensible after a while to stop the IV fluids as they may overload her body.

I'll leave others to answer on the legal side as I have no useful experience there.

Again, England rather than Scotland, but register her death, without a death certificate you can’t do anything to do with her bills and finance, And undertakers, and I am very sorry you are going through this

I'm not sure if it applies in Scotland, but here in England I used the Tell Us Once service on Gov. UK which simplifies a lot of the admin.
You have my condolences, my mother had the same final days as lie ahead for your mum.