1. I don't know how you'd do graphics with arc in general, but if you need to access mzscheme, anarki can do so very easily. If you want to access a scheme function named 'foo, just write ($ foo), or abbreviated, $.foo.
$ git clone git://github.com/nex3/arc.git
$ cd arc
$ ./arc.sh
Welcome to MzScheme v4.2.1 [3m], Copyright (c) 2004-2009 PLT Scheme Inc.
Use (quit) or ^D to quit, (tl) to return here after an interrupt.
arc>
(This is assuming you're on Linux. I don't know how one would go about setting up anarki on Windows or OS X.)
2. If I understand it correctly, mzc doesn't compile to native code; it just wraps everything up in a neat executable containing the mzscheme binary and the byte-compiled scheme code. There was some discussion earlier about getting mzc to work with arc: http://arclanguage.org/item?id=10157.
3. I haven't looked at picolisp. I do not think that a C implementation/hooks are particularly a long-term goal of arc, especially considering Arc is intended to be the "100-year language", although design decision are of course pg and rtm's domain. However, arc is built on top of mzscheme, and mzcheme has a C FFI I believe, so setting up arc to hook into C should not be impossible.
