First, congratulations for returning to school. That is a big and important step you took and something you should be proud about doing. I know it is a hard thing to do after being away for awhile (I recently returned to school to seek another degree after a 4 year hiatus).
To answer your 1st question, I became a member of IOTA as a full-time traditional student. I know, however, of many IOTA men who were non-traditional students that joined the organization as non-traditional students and are/were quite active. IOTA has the unique history of being founded by 12 non-traditional students with jobs, families, and recently returning from military duty with all of this occurring during the Civil Rights Movement.
I think it is important that you truly do some soul-searching before you seek membership in any organization to make sure that you truly have the time and desire to dedicate yourself to your membership on top of your other responsibilities. The timing of your quest for membership will also be important. "Dropping a class" should not be a priority....the organization that you wish to join will likely be there when the time is right.
I wish you well in your quest for membership. Peace be onto you.