Mine was on his feet independently at 8 months. I think new walkers/cruisers face the same risks no matter the age actually. I'd say corner guards on coffee/end tables, entertainment stands and the fireplace hearth (if you have one). Venetian blind cords and electrical cords, of course. And assume that he will climb sooner than you think possible.
Kids' heads are remarkably well padded with bone. They don't fall that far even when they tip over, so damage is limited. I think there is greater danger to the softer tissues, like eyes. I'm not sure a helmet would help much - a hard one might make him top-heavy and a quilted one wouldn't provide all that much cushioning. It's more likely to give your husband a false sense of security. Sorry, but the way kids learn is when things backfire and they get a little bit hurt.
Do what you do with any child - get down at their level and look around. I'd also look into one of those gated pens (bigger than a play pen) that gives them some room to move around. They can usually be configured in a variety of shapes to fit in your available room.