Waiting for OPT and got job offer, switch to TN?

Hi all!

I just recently graduated with a Doctorate in Music at USC in Los Angeles, and I filed for OPT in July. I won't receive it until October if it gets approved, but in the meantime I've received a job offer at a university (not a faculty or adjunct position, but a temporary full-time staff pianist position). The position starts this week and I have to start filling out paperwork tomorrow. Should I switch to TN, and if so, how would I cancel my OPT application? Ultimately it's better for me to be on OPT because I'd like to freelance. My questions are:

1) Because the position is not faculty, do you foresee any problems in getting approved for a TN? I can certainly ask my dean to write an employment letter that outlines that I will be playing, coaching and doing some teaching. Also I've got the terminal degree, have 6 years of university faculty teaching experience and have been in the US for 12 years.

2) What do I do to cancel the OPT?

3) Are there any options available for me to be able to start working while I'm waiting for my OPT? the 75-day waiting period ends in 10 days.

4) From LA, what's the closest border that I can process the TN?

Thank you so much in advance for your help!