Do I need to pay federal Income tax on the transfer of business interests described below?

If you sell the interests you will trigger a tax event. These things are generally done with mergers. You need hands on advice from a CPA.

Is it worth of pursuit lawsuit

Have you paid the entire purchase price already? We would have tied note payments to compliance with non-compete

Do I need a copyright lawyer ?

Why do you assume you have any rights to the music? Do you have a publishing agreement?

Is it legal for me to post nude/erotic photos of myself on facebook, twitter, youtube, etc. Note; I'm over 18 ??

Is it a crime, no. Will Facebook cancel your account and ban you, yes.

It might be a criminal act under a revenge porn statute, but I am not sure if Missouri has enacted one yet. Otherwise, when added together with...

How should I handle this situation?

You are being set up for a scam. If you met her on a dating site and she originally said she was over 18, it is a scam and someone will be popping...

And we're you contacted by someone who then said they were under 18?

There was a group on facebook created, and as a joke a picture of a man's penis, a google search image, was posted in the page.

No there are no legal ramifications but Facebook will probably ban the users involved. Why exactly is this funny?

Can I do anything about this?

Unfortunately, you are probably out the money.

What actions can I take? Can they use my money as a 0% free loan? Is this a criminal matter?

Do you have a written agreement? Did you lend them the money or make an equity investment. If you purchased equity you may not have a right to get...