Hi,
A quick answer and words of wisdom because you asked. Backup your entire dataset. Pick whatever date you want to login. It's just a label. We still see people logging in with some backdated date, thinking they are still in ACCPAC Plus.
And when you have time, as Bruce suggests, take a look at the webinars.
Do the GL first, and it will allow you to choose a date for the entry. Some people choose the Actual YE date as if everything magically was done on that YE date, or choose today, which actually tells you when you closed the Year. It doesn't affect the GL YE close.
As soon as you have closed 2012, you should open up the next year 2014 in GL.
As for closing out AP for the YE in Payables, this will just update the statistical numbers by year and this is not date sensitive. So simply go ahead and close, and you can at least get proper statistics starting to build for 2014. When you are prompted for the YE clearing date for clearing history, you should probably leave and do not purge until you have had your consultant look at the settings to ensure you have got the proper retention of historical data setup. Then pick up the purge properly with the next period end processing in AP.
Assuming you are current with your Adagio software maintenance (more words of wisdom), your current GL after closing the 2012 and opening 2014, will retrieve the AP data into 2013 and/or 2014 Ledger based upon the AP transaction date (if set up to retrieve by transaction date) because Adagio is that smart.
Best,
Brian