can you post a pic? I've painted a few stained doors. I cleaned it well, and sanded it smooth, going from 120, 150, and then a 220. wipe clean w/mineral spirits or similar. now coat it w/an oil based primer. you can roll or brush it on, or use the Zinzzer in a can. once this dries, you must fine sand w/a 220 grit. wipe clean and remove all fine residue. now paint. use a good quality enamel paint. if this gets any type of weather, you must use a UV type of paint meant for exterior applications. painted side panels is a personal choice

I'd prob have to go w/plum/purple. we just had this color on another post w/similar siding. I'd also plant some purple flowers and purple flax, along w/sage plant colors in the flower bed. like this this house below has almost identical siding. I'd also do a slighting warmer white trim. almost a canvas color do some of that purple slate tile on the front porch too. Black Raspberry, BM napa harvest lighter green shades would work too (the one below, do the side lites in the same green or white

Because of the trim, I actually like the dark door as is. Would not choose a pastel color because of the light gray siding. If you want a change, you might want to also at least consider a different color that also has a strong contrast such as a bright true white or a bold blue or dramatic red burgundy.. .

Leave the interior of both doors the same color as trim in house. Just paint the exteriors black, and your choice if you want to paint both of them.