Most door companies stock what you are looking for.

I say go for it as your door is the window to your home. My advice would be to consider the colour of the flecks in your brick to make sure your chosen colour works with it and not to forget about the colour of your roof and window frames. For example I would have loved a red door but it would have looked ghastly with the green roof on my 25 year-old house. Instead I did black with dark grey window frames (which truly just look black) which works to pick up the black in the brick. I added my big pot plants with green foliage and still got a touch of red in the form of an old chair I picked up from an op shop years ago. The entrance is welcoming, attractive and reflects what is waiting inside. Have fun and if your chosen colour isn't quite right do what I did and find a way of incorporating it into the scheme somehow.

Is it for yourself or guests? If it is for yourself, I'd store the shoes nearby (i.e. in the laundry if that's near the front door) as that entry is stunning and I think any furniture would take away from its beautiful simplicity. If it's for guests, then I'd consider getting a small stool and basket / box for when guests come over. Something really simple, but convenient for them to remove their shoes and pop them in the basket / box until they leave.

Side lights for sure and a straight door like To find and design pictured but I'd use clear glass, because the door is recessed which creates the privacy. Paint it white and at the same time paint the balustrade white to feature it again as was the idea when it was designed and return the front patio to red which I guess would be the original colour. Changing these great houses from original and think they look better is like getting an original XP falcon and putting a spoiler on the back because a spoiler looks good on a Porsche.