Hi All.
I am going to replace the head gaskets in my Subaru Legacy 2.0 GT 1990 (EJ20 engine) soon (classical Subaru overheating cause). It has already 192k on it. I've only replaced HD in a non-turbo Legacy (EJ25) so far and have a couple of questions:

1) what should I be aware of before replacing the HD in my car? What has has to be replaced as well? What should?
2) as the current HD are already pretty ruined I need to put water almost every 2nd day.When I start the engine I can hear the water flow in the engine while sitting inside. Is it actually normal? Could there be also a problem with the core heater?
3) when I push the car to hard it starts to kind of strongly pull and shake (in the direction of driving). It seems like this problem is fuel supply related (possibly fuel pump or fuel filter). Has anybody experienced that sort of problems?
4) is it possible to tune the turbo in a 1990 (EJ20) Legacy? One mechanic told me he wouldn't be able to use his laptop for that model.
5) once I was manually pumping the bigger hose (left side) while putting some water in, and some rusty water came out of the water reservoir. What could it be a sign for?