"Scantily" is the adverb form of "scanty"
scant·y
adj. scant·i·er, scant·i·est
1. Barely sufficient or adequate.
2. Insufficient, as in extent or degree.
"Clad" does indeed mean "clothed"
So someone "scantily clad" is "insufficient clothed". The phrase describes (typically but not always) young women wearing lingerie.
That is, typically young, typically women, typically lingerie.
I don't know the first citation of "scantily clad" but it has become a useful cliche in common use today.
It is generally risque, typically (but not always) erotic. It is often used to describe "glamour photography"
Glamour photography is a genre of photography whereby the subjects, usually female, are portrayed in a romantic or sexually alluring way. The subjects may be fully clothed or seminude, but glamour photography stops short of deliberately arousing the viewer and being hardcore pornography.
Summary
Bumfuck, Egypt is first documented in army slang from 1972, and BFE is from at least 1988. Bumfuck, [Egypt] appears to be the original, followed by variations Bumblefuck (1989), Bubblefuck (1993) and Buttfuck (1999).
Sometimes these variations appear standing alone, sometimes in Egypt, or Africa (also found in BFA), or another country, (rural) state or place, and sometimes prefixed by East or West. More recently, both BFN and Butt Fucking Nowhere are reported from 2002.
As Bumfuck, Egypt appears to be originally military slang, given the number of abbreviations they used I can easily believe it was also jocularly and euphemistically shortened to BFA before 1988.
Partridge
The Concise New Partridge Dictionary of Slang and Uncoventional English (2003):
BFE noun any remote location. An abbreviation of BUMFUCK, EGYPT US 1989
Bumblefuck noun any remote, small town US 1989
Bumfuck, Egypt noun a mythical town that is the epitome of remoteness. With variants US 1972
It also gives BFN and Butt Fucking Nowhere, both from 2002.
OUP
These 1989 and 1972 first citations are given with others in The F-Word (2009, Oxford University Press):
BFE noun [Bumfuck (or Bumbfuck), Egypt]
Military & Students. a very remote place; the middle of nowhere.
1989 P. Munro U.C.L.A. Slang 20: Troy...lives out in B.F.E....Bum Fuck, Egypt.
Bumfuck noun
Military & Students. a very remote place. --used with a placename, esp. in Bumfuck, Egypt. Also Bumfuckistan. Jocular. See also BFE, BUMBLEFUCK.
1972 Sgt. E-6, U.S. Army: They probably sent those records out to Bumfuck, Egypt.
It also gives Bumblefuck as a 1989 alteration of Bumfuck; Bubblefuck as a 1993 alteration of Bumblefuck; and Buttfuck, usually used with a placename, from 1999.
Usenet
I found an earlier example for the initials BFE in Usenet, on 11th September 1988 in alt.cyberpunk:
$600 is about what we paid for my first computer -- a C64, 1541 and printer; when I was a upper-lower class kid living in the backwoods of
BFE, Leesville, Louisiana. (Ft. Polk sux too. :-). We weren't on
welfare, but we weren't rich either. I think we saved about 9-12months
for the computer. (Grandparents bought me a monitor a month later. What
a rescue. :-). That computer made the difference between me being
a dual major CompSci/Journalism student in Houston instead of being
like my cousins: 2-4 kids, HS diploma at best, slow paying job, no future,
and living in BFE, Louisiana.
Best Answer
This is an older meaning of "so" that used to be very common in English but has fallen out of use, where "so" means "in this manner/condition". We still use it when we say things like "you do it like so", "just-so story", "it was so long (and you gesture with your hands to indicate out long)". Actually, the first three entries in dictionary.com seem to convey this meaning.
So, the "so far" part means "up to now" and the "so good" part means "it is good in this manner/condition".