If it were me, I'd avoid drilling 1/2" holes through the frame I-beams. Others will likely say the same. I'd consider some sort of beam flange brackets similar to the photo below. Could be a manufactured one or something you make yourself (if you can weld). Google "beam flange bracket" for ideas and sources. Easier, faster and non-invasive.
From a structural engineering point of view, you should be fine with drilling 1/2" holes. (Look at the huge hole they hack out for slide mechanisms.) Keep the holes in middle 1/3 height in the vertical webs of the beams, preferably in the center and sufficiently away from any existing holes. For steel beams in buildings there are industry standards for where openings are to be in steel beams. You could google that too for ideas. I'd stay away from the spring hanger areas as that is a high stress location and in some cases is where fatigue cracks occur.
For drill bits, maybe start with say 1/8" and then maybe 1 to 3 consecutively larger diameters. A 1/2" cobalt bit might be a good choice. Bits need to be SHARP! Use low drill speed and a little oil. A step bit should work okay too.
