I don't think it makes a lot of difference. The gsx.cfg file only overrides the data thats in there, which is not much more than the door and refuel positions. The behaviors appear between the internal profile and the GSX programming that PMDG seems to have built in, at least partly..
I only did a quick test (without the PMDG supplied cfg, for all it matters) and for me it DID load both the fuel and payload correctly.
All cargo doors opended and closed correctly.
1L door I closed and armed manually (intentional, freighter ops) but opened/closed correctly earlier.
There is a general GSX issue that, because no two services can be active at the same time on the same side, the stairs are removed when fueling is set on the left side. I think this should be looked at, to exclude the stairs from this rule.
Re: big fuel truck or small fuel hydrant: this is an (airport) profile selection. Yes when there is no undergorund refueling the big fuel truck clips to reach the refueling ports. This is more a general GFSX issue than 777 specifi I reckon, pathing of the big fuel truck could be improved.