NFC = Near Field Communication and is mainly used for Android Pay’s tap and pay function (though other functions can also programmed for it but most don’t use this function)
the Moto X 2nd had 2 GB of RAM and came in both 16 GB and 32 GB of internal storage
the Moto G4 Play has 2 GB of RAM and 16 GB of internal storage
the Moto G4 has 2 GB of RAM and came in both 16 GB and 32 GB of internal storage
the Moto G5 Plus has 2 GB of RAM 32 GB of internal storage or 4 GB of RAM and 64 GB of internal storage
the RAM is used for processing software code and the more you have the faster the phone may feel (though 2 GB is enough more than enough for most users)
internal storage is the amount of space to store the software and media you have (including the OS and preinstalled apps) with the OS section growing as fast as it is I would not look to get a phone with less than 32 GB unless it’s a budget phone that will not be using many apps on
edit to add
when you say 1 GB do you mean you have the 1 GB Refund plan ($25 - unused data refund) the new phones can not uses that plan there is still a 1 GB plan for $20 but no refund and if you didn’t run out of data before you should be find on the 3.0 1 GB plan