None of that is reason to grant you Weingarten rights. WR are very narrow in scope and not something to which you are entitled just because you are uncomfortable, dislike the guy you are meeting with, think/feel/know someone in the room has lied in the past, or because they intended to hand down a suspension. If it is a done deal, you aren't entitled to have anyone present. If you start screaming about your rights the second you walk in the door, especially when you are wrong, no one is going to be inclined to help you.
Once again, your employer is not a court and doesn't have to prove you did XYZ to fire you. Even with a union, the legal standard does not change. This is not criminal court. You are only entitled to due process as set out by your CBA, but in the course of that process, the employer may still determine they don't want you working there and they may still not have proven a case against you the way a court of law would have to do. Honestly, the more you drag this out and cause a fuss, the more convinced the company and union are going to be that their initial decision is for the best. No one wants a disgruntled, difficult to work with, demanding even when flat out wrong, employee. You said pages ago you don't even want to work there any longer. At this point, you are your own worst enemy. Let it go. Move on. Rebuild your work credentials as I doubt you are going to get a positive reference from these folks. Is it really worth the fight for a job you don't want?