This might be an expensive lesson in tax liens on my part, but I am learning more and more every day.

Right now is when you will learn one of the greatest lessons in investing: How to raise capital fast when you need it. 

I think I may have been better off had I never tried to negotiate...So what's my lesson here?

Even if your profit ends up lower than expected, you gained a lesson in due diligence.  

What if she wanted you to sign up for ballet lessons because she was really into them but you didn't want to? 

Expensive lesson learned: put contingencies in your offer unless it's a steal.

Would this be more of a syndicated deal or a private lending situation, or are these more or less one in the same when attempting to attract other investors ? 

Multiple offers are lessoning and days on market are increasing.  

You will have a great civics lesson once you start

The garage unit is the most difficult to complete and make legal, so I would abandon it and get the 3rd unit into compliance.The lesson here is to VERIFY facts that you will or do depend upon in your offer to purchase.