Now, it is my understanding that safedocks come with GSX
Yes, but only for FSDT airports. They are the only ones that use GSX safedocks right now.
(or, gates will have "the person with the bats" instead).
That would be the "marshaller", and it will work with every airport, default or 3rd party.
So, at UK2000 CURRENTLY, only a few gates have safedock (T5 plus some of T3). If I get GSX, will:
-Every gate with safedock have safedock
Nothing will change regarding safedocks. On a 3rd party airport that already have its own safedocks, you will still using them just as you were before installing GSX.
GSX will add a marshaller in all other gates when the airport didn't provide any docking aid.
In fact, you will also have to tell GSX which gates (or terminals) of your 3rd party airport already come with a safedock, so GSX won't display a marshaller there. This can be done with the supplied scenery customization editor.
-It be able to recognise a 777 (doesn't currently)
It's not very clear which 777 you are referring to, and what do you mean with "recognize".
If, with "recognize", you mean a safedock in that airport that didn't recognize the 777, installing GSX won't change anything because, as I've said, nothing regarding safedock will change with GSX, they would continue working (or not) as they were.
If, instead, with "recognizing", you mean that GSX would be able to properly service that airplane with its own service vehicles, GSX currently support the Captain Sim and PMDG 777 models. And of course, you can create a configuration for any airplane, using the integrated airplane configuration editor included with GSX.
In addition, I would like to ask/confirm: If I buy a new airport already "released", will it update the GSX for me ? Not sure which airport you are referring to. If I buy a newly released airport, will that come with a system wide update?
I'm not sure I understand you. GSX will work on any airport that has a valid AFCAD file. It doesn't change anything to it or "updates" it. If the original developer would release an update of such airport, as long as its AFCAD file doesn't contain errors, GSX will continue working on it, without any need for other updates.
And, you can further customize how GSX work over any airport, using the supplied scenery customization editor, which allows you to start from the data already present in the scenery AFCAD, and build upon that.