As for point 5, Arc uses certain characters as syntax abbreviations iff the special characters occur in what would otherwise be normal symbols (to the Scheme reader). So far, there's

.a ; is the same as (get a)
a.b ; is the same as (a b)
!a ; is the same as (get 'a)
a!b ; is the same as (a 'b)
f&g ; is the same as (andf f g)
f:g ; is the same as (compose f g)
~f ; is the same as (complement f)

where

((get a) b) ; is the same as (b a) by Arc's indexing
; e.g., ("abc" 0) is #\a
((andf f g) x) ; is the same as (and (f x) (g x))
((compose f g) x) ; is the same as (f (g x))
((complement f) x) ; is the same as (no (f x))

See arc.arc for the actual definitions of these operators.

There are precedence and associativity rules, such as

a!b.c ; is the same as ((a 'b) c) because ! and . are
; left-associative
f:g:h ; is the same as (compose f g h)
~f:g ; is the same as (compose (complement f) g)

To explore these more, you can use the ssexpand function in Arc:

arc> (ssexpand 'a:b.c!d)
(compose a b.c!d)
arc> (ssexpand 'b.c!d)
((b c) (quote d))