Converting from Numbers '09 to Numbers 6.0 for MacOS

I have been a user of Numbers from the day it was first brought out as part of the iWork package, maybe 2007? All my spreadsheets are currently in Numbers '09 format. Over the past couple of years, I have tried to update some of these to Numbers 6.0 but have run into annoying issues that always sends me back to using '09. Simple things like trying to get the date to format as yyyy mm dd. I have tried to make a custom date format but it does not seem to reformat text entered as 2020 02 04 to 2020 Feb 4 (as '09 easily does). I have also struggled with adding rows where formulaes are part of cells. The format of columns does not seem to be carried into the new row so for example, formulaes that including summing of columns have to be manually entered each time a new row is added.

Where can I find a clear, easy to read summary of all the changes that have occurred during the evolution of Numbers and how to do things in Numbers 6.0 that seem so easy in Numbers '09?

As you probably know, using Numbers '09 on more recent OS versions crashes if things like changing sheet or table names by double clicking is tried!

I know this post is a bit of a ramble but Numbers was a great application! What happened?