I think a useful path to solidarity is that almost all of these things are promoted or exacerbated by the same antagonists and that unifying against that shared enemy is the best tool to counter them. Taking power away from the hyper capitalists advances all these goals. If we get to the point where any one of them isn't that much of a concern anymore and people who were only in it for that start to peel away we'll have made pretty good strides towards all of them. And by then hopefully they'll have come to care deeply about the struggles of the other groups and continue on.
We don't need to figure out what the #1 problem is when we all have the same villains.