Troubleshoot launchd/launchctl issue where application won't load
Got it solved. Will leave this question here…in case someone else has similar issue…and in hopes that someone can offer some good ideas for troubleshooting launchd/launchctl in the future.

My problem was I didn't have my mongod.conf file in the right place. As per plist directive launchctl (or is it launchd?) was looking for /usr/local/etc/mongod.conf but couldn't find it, so, it "loaded" mongod but the app never actually started...and there were no errors to that effect…that I could find.