I know that part of the paint blister / peel problem is if you paint in weather that is too hot or cold. I don't know the guidelines for proper temperatures but I know it can be an issue. I would think any exterior paint would work well on a primed door.
I don't see why you couldn't use a roller with a proper nap - but if there is a raised panel, you may want to brust the inside corners of the raised panel - brush does a better job on that.
Not sure what you mean ...are you talking about he inside edge of the door where it closes against the opening of the door frame (the weather strip question) I would roll that too and make sure it is really dry before you attach the door and open and close it. What color are you painting it?
Since you are in Tellico Plains and it does get colder up there I would recommend an additional primer coat (Zink) and a good exterior paint in the color of your choice the weather up there can be harsh on steel . you can do it with a roller , however a bit of tape and plastic and a power painter would give you a better finish and better coverage and last longer for years to come .
lol back in the day when i was a lad I put the new 18 inch line to the trout hacheryup there the fresh water line that feeds the hatchery that is . thats how i know where your at stoped at the hardees at the bottom of the Mt. in town every mornin for a sasuge and biscut and up to the top of the Mt. till night took 6 month to get it all done .