After owning a few Bromptons over the years, and talking to a lot of other owners -
headset is not the 1st thing I'd worry about.
-It's nice that Brompton includes a pump with most models(except superlight/titanium).
But just like most portable pumps; it sucks. I carry a Topeak Morph G.
-Depending on you weight, how much you stand, masher or spinner; right/drive side pedal
gives up too fast for some. Some in as little as three months.
MKS ESPRIT SUPERIOR PEDALS by
1nterceptor, on Flickr
-Front carrier block is a very useful option. Can accept many kinds of luggage; big or small.
I'm using a Demano messenger bag since 2013: