1) The only time the executable is not already in memory is when you type "perl script.pl". If I do a perl -e 'print "Hello World\n";' from my CLI it responds in an eyeblink. This leads me to believe that the only serious overhead concerns are related to interpretation... hence my suggestion that
2) You can keep a script in memory by using a while loop, or you can set up a controller script that uses
the other scripts you want precompiled and starts one of them up on command.
3) Check the FAQ
for more information on compiling scripts and reducing the size of your perl executable.