DEBUG_MESSAGE(" ");
which prints out the message below the problem.
For macro files which will be used in lots of places you can use
WARN_MESSAGE(" "); which is just the same as the debug message but suggests that the message should stay in place permanently to guard against bad input or other unexpected states.
The perl command "warn" also works but is somewhat deprecated since it has perl behavior unmodified by PG. It can be useful when there are syntax errors because syntax errors currently disrupt the DEBUG_MESSAGE system.
For 1 and 2 you can checkout the standaloneProblemRender --
Definitely SAR at the moment, but perhaps you can help with that. :-)
Slightly closer to being ready for prime time is sendXMLRPC.pl in webwork2/clients/
With a little more work these two scripts can be somewhat disentangled from the webwork2 code and permit one to install the pg code and the editor and edit files locally.
One last trick is the "it's all text" add-on which you can use with firefox. it allows you to edit textarea text in the editor of your choice.