Agreed on all counts. I tend to find people don't think highly of Edmure because of Robb's plan being foiled (which, like you said, is Robb's own fault), Catelyn's low opinion of him (she's made a lot of mistakes as well) and that business with his father's funeral boat, but he seems like a good lord to me.

And really, holding back Tywin's crossing was a great military feat in itself as I had the impression that Edmure was very outnumbered.