I don't know how many turns as of recently, because I was the one sitting in the car watch the tach the last time the idle was adjusted.
It does respond to the changes in the idle screw.
Ok so since it responds to changes in the idle mixture screw that means you're not bypassing the idle circuit. The idle at 1000 is a little high. It should turn smoothly at 700-800, but that's a finer point to deal with later.
Here's the deal. These symptoms are most likely fuel starvation of some kind. The usual suspect is the fuel filter, but if you have replaced the fuel filter and the vapor separator then that leaves the fuel uptake sock in the tank, the fuel lines, or the carb. The carb is obviously more complex than the other components so it's got more possibilities for clogging or mis-adjustment. If you are going to run a carbed car these days you pretty much have to learn how to deal with it one way or another because most mechanics don't know spoob about carbs. I guarantee that most of these old Subes went to the junkyard because of the carb.
Everyone has given good suggestions, but we're just kind of shooting in the dark with the remote diagnosis unless we can rule out the carb. The Haynes manual pulled the carb rebuild section straight from the Subaru Factory Service Manual (FSM), so you can easily do a full rebuild with the manual if you follow the instructions carefully. I get my Beck & Arnley rebuild kits from Autozone for around $30. I use aerosol solvent, compressed air, fine wire, and a wire brush for cleaning. The rebuild kit comes with a little scale for adjusting the float. Just be meticulous.
Jonas mentioned a Weber upgrade...always a good option if you can afford it. It will need to be tuned...again it's just a matter of following the instructions.
It's possible that you have a vacuum leak that is leaning out the fuel mixture too much after the choke disengages, but that is difficult to fully diagnose without being able to eliminate the carb as the source of the issue. Ultimately, your car is completely dependent on the state of the carb, so I highly recommend you dig in. It's not as hard as it seems. Once you do it you'll realize it's not that difficult. I rebuild my Hitachi about every two years and it runs great. It's just a fact of life with a carbed car.