First of all, welcome back!
I think the main point to bear in mind Jasper is that you are identifying the things that bother you and addressing them as best you can. No, you won't get the answers you need right away, but yes, I think you are on the right track. As to the specifics, here are my views for what they are worth:
1) Paulie: No one should have to deal with mockery and ridicule, and if that is what your brother has on offer I would definitely stay clear of him. But perhaps there is more going on than you see right now. If it were me I would probably try to avoid the ridicule but leave the door open for future contacts if he changes his ways. He is, after all, your brother.
2) Criticism: You are in a tough place at the moment, and quite understandably it is making you emotional and sensitive. How could it not do so? But bear in mind that this is a website and that a text on screen may or may not convey what someone really means. It is really easy for things to be misunderstood. And if someone is in fact critical, fine. The same thing happens in real life. There is also the fact that not all of us can help or appreciate all the others. We all have our boundaries and limitations. I would try to focus on the people who are genuinely able to connect with you and not pay a lot of attention to input that may be less helpful.
3) Memories: That's a big one!!! Your T will be the best resource here, but as a rule Jasper, I would suggest that the path that will bring you the least pain is to accept that the memories do fit together and that they are probably accurate. The issues and details you can bring up in therapy. Personally, I would rather accept the validity of the memories, no matter how terrible, and then discover that they were false, rather than deny everything and then discover they were true.
4) I have had that feeling of being outside myself, but have never been frozen in place, except - as a teenager - when trying to sneak back into the house late at night, and as an adult by back pains! Seriously, it's not crazy stuff. It is you trying to cope with some terrible things that happened to you years ago.
I think it is normal to feel frightened by all this. But I also think it's great that you are able to get all this out on the table and talk about it. Surely that is a great step forward in itself.