It's not imperative for the first four, which were deliberately published out of chronological sequence and were meant to be standalones only loosely connected by a theme. So those four can be read in any order, as long as they're before the other four. Indeed, I don't think Seize the Fire has any impact on anything else in the series, and The Struggle Within, alas, has very little impact (basically just solidifying who the members of the Khitomer Accords are). Indeed, one could make a case for postponing Rough Beasts until just before Plagues of Night and Raise the Dawn, because those three essentially form a trilogy. Not to mention that PoN overlaps the events of the preceding four books chronologically, beginning at the same time as Zero Sum Game, so one can't really do a strictly chronological reading without going back and forth between books.