This may be a little out of context .. Sorry for that .. just wanted to register few of my thoughts.
1. Doing shrardha with the help of book is not advisable as the procedure changes for each veda, sutra and sakha. For example the count of grass blades differs with a tamil brahmin and people from telegu background.
2. Any errors arising out of pitru karyam will have serious impacts than errors happening with Deva poojas. If the shrardham is done with the help of an aacharya or purohit , he becomes responsible for the errors and the impact of the errors will only reach him.