One of my favourite jobs is stripping down old doors but that one looks like a real challenge to me, as Sparkwright suggests, you might want to replace the door. They're expensive, though, and your door looks original to the property so i'd make every effort to save it in this case. You can't remove it for the job, unless a replacement is available, so be prepared to put in the time to make it look good as new. A good metal polish will bring out what looks to be a brass doorknob but the wood around the door should be replaced rather than filled.
Personally, i like the colour of the walls but you can get good paint for the window sills from Johnstone. I renewed mine this summer and two coats did a good job. I think your upvc windows could do with a clean, too, and a soft copper wire brush dipped in clean spirit (not turps) can work out those marks with gentle brushing.
Hope the weather holds out for you.