My suggestion comes directly from experience:
Lay the flooring first.
Take advantage of the "extra space" that you have without any baseboard and
use that space as your required gap area!
You never know for sure when a plank might end up a "gnat's hair" (or more)
short of the distance that the baseboard (or shoe moulding) might cover.
With the baseboard *not*
being in the way, you'll have the extra advantage
of being able to knock off the *bottom*
of the wallboard where necessary to
get your "gap space" should you end up with a plank or two or three that's
just a bit on the "long" side.
Then, once all the flooring is laid down, go ahead and replace the baseboard
to the new height of the floor. With good fortune, you'll have no "holes"
beyond the baseboard face, but if you do, you still have the "option" of
covering over the "error" with the extra moulding -- something you might not
have if the baseboard goes down before the flooring is laid.
Assuming "good fortune" holds fast, you'll end up with a better-looking end
result by having the full height of the baseboard show rather than it being
visually "chopped off".
Also, consider that with a router, router table and the proper bits, you can
very easily mill your own mouldings -- of whatever thickness you want or
need. Considering the linear-foot cost of store-bought moulding, that could
well be economically viable!
And Last, you're cutting it too short on the amount of flooring you are
buying vs. the given sq-footage.
Might as well admit it now than regret it later -- you're gonna make a
"goof" in cutting somewhere... probably several goofs. They add up fast. You
will also want to have at least one or two cases of unopened flooring left
over as a hedge against the unlikely need to replace some pieces over the
next 15 or 20 years. Many installation house will recommend over-buying by
about 20% -- do what's comfortable for yourself, but *do*
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