I'd get the bars first, for no other reason is that bars tend to be more or less forever. Start getting used to the narrower bars ASAP. IMHO, position on the bike (including bar width) is what you sort out first prior to messing with aero wheels and helmets.
Besides, the benefit of an aero helmet for mass start is tenuous at best. Not nearly as clear cut as for individual events or sprint.
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Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --
the tiniest sprinter