I've worked with lawyers over the years and while you can find plenty on this with google, I can't condense that to fit in this text box. So back to google for you and consider that your new system will be just that. Nothing you will sell them until you've been at this a few years.

One thing. You have to decide if this will be standalone or web based. Given how much leaks today, those cloud systems may be a bust. That is, the Panama Papers.

Also, here's a thing. We haven't quite reached the point where computers and AI automate this. Maybe in the future but for now you do this work. Since you do this work you automate what you can.