What are the legal implications of being charged with a felony for carrying a concealed weapon without a permit and then having adjudication of guilt withheld?

Usually, that kind of result goes hand-in-hand with a diversion plan for first offenders, in which you'd have to be on probation, essentially, usually for 18-24 months.  If that's going to be your situation, you need to do whatever is necessary, to comply with every requirement of the program:  show up on time, pay the fees (there's almost always something, although your program wouldn't necessarily include substance abuse testing), whatever.  If you complete the program successfully, the charges against you will be dismissed and your record will be clean.  If you don't, you'll be found guilty of the original charge, and sentenced accordingly.  The choice should be a no-brainer.