There mostly aren't physical barriers. Unlike nukes, where you need specific materials and equipment that we can try to keep tabs on, bioweapons can be made entirely with materials and equipment that would not be out of place in an academic or commercial lab. The largest limitation is knowledge, and the barriers there are falling quickly.

On your second point, see my response to oceanplexian below: https://news.ycombinator.com/item?id=47189385