The Calendar in FMGo is the standard Calendar for ios devices. There are third party calendars available. User PhilModJunk has one that he created. I can't find a link to it yet, but If I do I will paste.
Not all scripts steps are available on FMGo. You will have to post a copy of the scripts.
I have too many scripts to do a paste here, is there a list of the script function that are not available on FMGo13?
Would converting the FMP12 file into FMP13 file helps it run smoothly on FMG013?
No, converting to FMP13 will not help it to run more smoothly. 13 and 14 have some added script step that add more features, such as different type keyboards.
Here is a link for script step compatibility
Here is link to FMGo development Guide