Tips for painting exterior doors?

[RoxMonster]

We're hoping to get our siding painted this summer and we'll be painting the exterior doors (front and back) ourselves. They are currently a cranberry-ish red and we would be painting them something like this:
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(Fabulously Grape by Sherwin Williams)

Any tips? I have read some places that say you should sand, some places say you don't have to. Some places say to not paint the edge of the door (that closes) because it may not close anymore in humidity, but I also don't want red showing when the door is open.

I was going to get the exterior paint from SW. Do I need separate primer?