Looking forward to seeing your new boat!
Not sure, but I think anyone can input the MMSI which will be sent to you but, IIRC, you only get one chance. If you get it wrong the set has to go back to the supplier to be reprogrammed. Have I remembered that correctly, Superradioman?
You need to display your ship's radio licence (not licence to operate) on, I think, the port side. That's all there is to it - until next year when you'll need to renew it - they will send a renewal notice to you. We always carry our licences to operate when we are on the boat (in an Aquapac bag with other important stuff).
The SSR is needed if you intend to use your boat abroad and, as far as I know, your £12 covers you for as long as you have the boat.
The CG66 is free and I can't see a reason why anyone would not fill it in.
Don't know about Part 1 registration!