You're welcome. I'm living vicariously through you because I know I won't be able to buy another bike any time soon.
Here's my $0.02
Seatpost: Yes. These are really common, and they can help to quiet street vibrations. Your frame will quiet much of this, but it would pretty rare to find a CF bike with an AL seatpost. They're cheap and worth it, IMO.
Stem: Maybe.
Bars: Maybe. I don't think you need to worry about strength. You shouldn't be putting too much weight on your bars anyways, so I don't think that would be a problem. Some CF bars look really comfortable, and many people swear by them (I don't have them).
Good luck. When it comes down to, I don't think you need to worry about strength on any CF parts in particular. If you want all the CF you can get, just get it, especially if you're riding in normal conditions. And, honestly, 220 isn't too much. You're a clyde, but you're on the leaner side of clydes (I'm 265).