1) Not only is B1-9 available, but so are all
of the modules that make it up in their full
forms. B1-9 offers three adventure paths,
of which the one that is most friendly to
starting adventurers is the one that starts
with Caldwell's Castle and continues with
The Hall of Rock and The Great Escape and
then on to the common ending in The Veiled
Society, which has a recommended sequel of
X1 The Isle of Dread. Alternatively, B10
Night's Dark Terror would be another good
sequel.
2) The classic B2 The Keep on the Borderlands
is another good starting point -- better than
Elwyn's Sanctuary that precedes it, as the
latter is meant to be taken out in one go
and includes a couple of monsters that are
much too tough for a 1st level party. For
this path, I would start the party out at
Castellan Keep, have them take a side trip
to Elwyn's Sanctuary after they have gained
a couple of levels, and then take on the
Hobgoblin King adventure after they have
finished cleaning out the Caves of Chaos.
3) DDA1 combined with a mini-adventure in
the Dawn of the Emperors boxed set make a
good starting point for adventurers based
in Thyatis City. DDA2 is not available in
PDF form, so the next best sequel woul be
Rahasia followed by The Lost City. The
first adventure in Wrath of the Immortals
would be another good prequel to Rahasia.
4) The next best covered region for Basic
level adventures is Thunder Rift -- if we
locate it an obscure valley in the Old
World region rather than an alternate
pocket plane, that region has a lot to
offer low level adventurers.
The various gazetteers, if used as source
material for adventure paths, would leave
us with a lot of work to do fleshing out
the adventures. The Karameikos based
paths could be fleshed out with the
adventure outlines in Gaz 1 that do not
too closely match the actual adventure
modules used.
Finally, I would advise against using the
Savage Coast, the Hollow World, or
Undersea as initial adventure path
starting points -- they would require
coming up with too many variant rules
to make easy starting points even if they
had good 1st level adventures.
Anyway -- I have been assuming that the
logical starting point for a low level
adventure path would be Karameikos and
thus have concentrated most of my work to
date on that region. However, if there
seems to be more enthusiasm for an
alternate starting location, I will
shift my attention to whatever region
has people doing the most work on
adventure conversion or creation.