This. This is what is in the back of my mind in this 60 year old house. Often when I peel back a layer to do something, it reveals issues. I call this a Frankenstien house due to each generations of unrelated modifications. I'm thinking/hoping this should be pretty straightforward though.
One or two in progress.
You can make your own here: https://creator.nightcafe.studio/create, however to actually make the footage usable (editable), you'll have to download the raw file and process, stretch and up-rez it. I use Topaz Video Enhance AI and AfterEffects for that. Still images are...
It looks pretty straightforward, but I know nothing of such things. Buy a pre-hung door of the right size, and have someone pop the old one out and the new one in? Barring unforeseen problems, it looks fairly simple. It's a 'regular' front door. Anything to look out for?