Sorry you're going through this stuff JNChell
Adding family law court to a BPD relationship can really increase the stress.
Only a lawyer can answer legal questions, and no one here is a lawyer (and if they are, they can't offer legal advice).
There are some things, though, that we've experienced that might be similar where you live, for comparison.
1. Since I legally signed the vehicle over to her, is it unlikely that FC will take into consideration the way in which she underhandedly did this? Also, is time a factor? This happened around 2 years ago.
Courts seems to care about two things. One is the pattern of behaviors. Something that happened a long time, and is only now surfacing as an irritant, and for which there may be no evidence (he said, she said won't go far), isn't likely to make an impression.
2. Do any of you have any experience with having access to their social media during discovery, and how did it affect your case?
This will depend on content (e.g. what it says -- whether it's about the minor child or something else), where you live (every state has a different set of laws and each judge/county may have a different way of interpreting those laws).
If you are trying to use her social media to show that she's mean to you, court isn't likely to care. For the most part, family law court looks for behaviors that impact the kids.
What I learned is that judges see squabbling bickering adults every hour, every day, day after day. So when someone shows up who is solutions oriented, it really stands out. For example, if your approach is to say, "Here is the problem. We cannot seem to resolve this, though here is some evidence of the ways in which I have tried to work this out. How about we do this so that we don't end up back in court again." Then think carefully about that solution and how to phrase it so that the solution works even if your ex doesn't comply.
People here are great at listening to solutions you might want to propose, and helping you think them through.
4. Is she allowed to force me to pay CS, but not her ex-husband? They have a D8 together.
Why is the exH not paying child support?
How old is your child/children? Child support is a calculation. Do you know what kind of custody arrangement you would be going for? And how much it would cost worse-case scenario/best-case scenario?