2) A useful thing could be a "chat invitation" which, as the title suggests, is an invitation to chat. You just send one to a friend and on their screen there will be a 1 over the PM icon. Once they click the chat invitation, there will be an option to accept or decline it. Accepting it will send them to chat and declining it will keep them right where they are.
3) Putting videos onto forum posts. It will behave very much like the pic/gif thing. You upload a video, and it will have en embed code. You can put the embed code on the forum and there you go.
4) People can still see locked member's profiles as long as they became to old or requested to lock. If the member was locked for breaking the rules, the profile will become hidden, just like it already does.
I honestly can't say anything without sounding like a troll.