The level of PI insurance should be properly apportioned to your turnover, if you do 300 or more domestic PIR's over a year, I would want more cover than if I did 4 PIR's in the same period. I have 10 million PL insurance and PI for 1 million, the 1 mill deal was more expensive than the 10 mill PL, it is also hard to find those who will insure for such levels. For a DI doing only domestic I would think 250k is enough, providing you are competant to give advise and services that meet the clients requirements. One idea and this goes for all who do PIR's and such like, write up a document like the ones banks and insurance companies give, you know the ones, they go along the lines of identified needs, and requirements, followed by your advise or actions given by the clients needs, get them to sign so they except that advise (with its limitations). This allows you to aportion some of the blame to the client if there is any discrepencies at a later date. Your liability will be determined by the level of advise given, but the risk will be shared by the client and will reduce the total amount payable under such a claim against you.
The most important thing is to fill each and every report, EIC, MWC and PIR with as much detail as possible, I always give at least 3 if not 4 pages of information with all my PIR reports, which include why I have given the codes I have given.