I'm so sorry you're going through this. I've done it many times (I've always rescued older dogs) and it's never ever easy.
It is, however, the kindest thing you can do.
For your dog, give them everything they could possibly want over the next few days - all their favourite food, favourite walks or trips out, favourite programme on TV, lots of cuddles.
For you, try and savour every single one of those minutes over the next few days. Take lots of pictures. Laugh when your dog something funny. Watch them when they're sleeping. Watch them plod around the garden. Remember really happy times. Talk to them about those happy times.
Definitely ask the vet to come to your house.
On Friday, please stay with your dog throughout the procedure however hard that might be - don't let their last moments be spent wondering where you are.
After it's happened, be kind to yourself. Whatever you want to do or where-ever you want to go, just do it. If you need someone with you, ask someone. If not, it's okay to be alone.
When the dog has gone, do whatever feels right for you. If you want to keep all your dog's stuff out for weeks/months, that's completely fine. If you want to put it away and deal with things later on, that's also fine. There is no right/wrong way to deal with things.
I, personally, always try to plan something for the day after a dog has been PTS so I can get out of the house and take my mind off it for a bit. It's horrible coming back to an empty house but I couldn't cope staying in all day. However, if you want to be at home that day then please do.
There's no right or wrong and, to some extent, you can't prepare for this stuff. See how you feel on Friday and do that.
I'm so sorry for your loss.