I started out as a steel detailer but haven't worked in that sector for over 10 years, so I've not got my finger on the pulse. But in the design sector I'm in now, it's a bit quiet at the moment and has been for a few years, and that means there are a lot of experienced draftee's out there without work - left overs from the boom times. So in that regard, it might not be the best industry to pursue at this time. But if you can leverage your existing skills and contacts etc, you might be able to get yourself into a niche, and then you would be set.

Regarding programs, Tekla Structures is the gold standard for detailing steel structures, but the price is up there (if you're looking at going it alone). Cheaper options that I haven't used are available from Autodesk for AutoCAD, and another from Bentley for Microstation. I would look at the Microstation option first, because the "core" seems to be better for 3D work than AutoCAD. However, Autodesk does a reasonably priced bundle of programs for the construction industry, which includes some BIM staples like Navisworks.