I have anger issues, though I just about always keep them in. Sometimes a word or even a sentance escapes my mouth but that's it. I feel very vulnerable in therapy. I mean, I know that if T hurts me, I'll do one of 2 things: a) just stop caring about him and our work alltoghether, turn around and leave and think about it a year or so from then. Or b) distance myself from my feelings and invalidate them until they catch up with me. The former ends up with me being angry at myself, the later being angry at T to a completely dispaportionate degree. The only alternative is to voice my concern and I don't generally feel my voice is reasonable, I feel my position (anger) is never justified and must always be sacrificed towards whatever the other person wants, because their demand must be more reasonable than my anger.

I don't like being vulnerable, but I am now at a point where I either go through the pain, or live in a limbo of anxiety, fear, anger and foresaken hope. Doing it alone just isn't an option for me, as the anger has a destructive potential that goes well beyond destroying my own life.

So yeah, I sit in T's office without much of a plan. With my former T, I would not be myself. But with this T, I am. If I don't want to look at him, I don't. If I want to be silent, I am silent. I really just have one rule: what I say must be truthful. I cannot lie. So I'll answer questions in a streightforward way, without much emotional content. But I allow myself my natural body language, which probably gives the context more than my words would anyway (also, using emotional words makes me feel pathetic, and that makes me angry). It's not so much about being vulnerable with him, to give him an open door to harm me, but it is about me being vulnerable to myself, allowing myself, what I never allow myself, to at least (and that's what it boils down to mostly) not look at him when I don't want to.

Regarding your questions:
1) Can I not be emotionally open from a place of strength rather than defenselessly and helplessly vulnerable like that?
No, I don't think so. If being yourself makes you feel defenseless and helpless unless you are some form of your angry self, then how would you be emotionally open without feeling defenseless?

2) What is even the difference if any, between being emotionally open and being outright vulnerable?
Vulnerability is one emotion. But as I understand for you, that being emotionally open equates to feeling either vulnerable or angry, I think for you, for now, there is no real difference. Vulnerability is a reaction to being emotionally open, so when you are one, you are also the other and thus, it feels like they are synonymous, even though for many people, they are not.

3)How much opening up would be seen as actually being vulnerable?
Vulnerability is a feeling you have when you are emotionally open in some form. So if you feel vulnerable exposing 1% of your emotions, that can already be seen as being vulnerable. It's your feeling, and as soon as you feel it, it is so.

4) Would I be expected to self-soothe if someone does choose to attack me in some very personal way when I am being vulnerable to them?
Expected by whom? Every person may have different expectations, what is important is that you find someone who's expectations don't negatively impact your progress. A T should help you, right? Whatever that means. Of course though, if you get angry at a T and were to attack them in some way, it would be good to previously know where their line is.

5) So to decide well as to whom to be vulnerable with, I would first need to be really really in tune with all my feelings and soft side?
No. Decisions can follow feelings, same as feelings can follow decisions. You can decide to be vulnerable and ignore your fear to a point, if you want to give that a try.

6) So what does an example of vulnerability based in strength, standing in your truth, warts and all look like?
Let me know when you find out

Hope some of that might make some sort of sense.