w.r.t issue #1:

If this is a vote, I vote for n-ary arguments. There are reasonable arguments either way.

w.r.t. issue #2: fl*+ vs. fl+*, No preference.

A bug:

"
(flround x)

Returns the closest integral flonum not larger than x rounding to even when x represents a number halfway between two integers. (C99 round)"

C99 round explicitly rounds away from zero. Use nearbyint with the default rounding mode set to nearest (which is the default on many systems already) to get rounding-towards-even.

A nit:

"
(flhypot x y)

Returns the length of the hypotenuse of a right triangle whose sides are of length x and y. (C99 hypot)"

Should be "...whose sides are of length |x| and |y|..."

...and I'm still looking closely for other issues.