EJ20 Turbo rebuild Legacy 1990 and some general questions

Hi Guys, I know this post is a bit unsystematic but I'm kinda in hurry now. Me and my mate, we're going to fix my 1990 Subi which overheats badly (head gaskets). The surgery of the car will start tomorrow! So I would really appreciate some good advice and info.

We're planning to replace the head gaskets in my Subaru Legacy 2.0 GT 1990 (EJ20 engine). The engine has 192k on it.

Before starting this huge but exciting action I would like to ask a couple of questions specific about rebuilding of the engine and some general ones:

1) what should I be aware of before starting to rebuild that engine? Which parts should be replaced as well? So far I got a new radiator, and planning to get the heads and engine block surfaces polished. I'm thinking about getting a new water pump, a new t-stat and probably a new clutch and a timing belt.

2) as the current HD are already pretty ruined, I need to put in 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 too 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?

6) I'm also thinking about replacing the clutch as changing the gears is not that smooth. Especially from the 1st to the 2nd one. It's really abrupt in comparison to newer Subis. Does anybody know whether it is normal for a 1990 Legacy? Or whether the clutch just has to be adjusted?

I would appreciate any advice and information on these problems.

Cheers.