Which date should I use for my first transaction?

Start it on the date of the first personal transaction. But if it were me, I would actually start it at day 1 of the financial year the first transaction occurred in.  So July 1st of whatever the year is.  Then on the off chance some earlier transaction needs to be slotted in - you can. I can see no obvious downside to having a somewhat back dated start date. But as the setup explains - you cannot alter it once it is done.          

I recently started a new ReckonOne Book for a family members sole trader business,  with a view to entering transactions from January 1st this year. I have started doing this, but I set the start date to July 1 2017. I thought I might get enthusiastic and go back and put the last 6 months of transaction in as well, so it has the entire financial year. But if I never get around to doing this, the gap of 6 months between start date and transaction one will have no obvious negative effect that I can see.   

The only thing that is stopping me putting in all the historic transactions is the tedious transaction entry process in ReckonOne.  It does not even have the ability to copy or duplicate repeating entries. So it takes forever to enter stuff.

Hope this helps...