Squeal doesn't necessarily mean new ps pump needed.
Swap/flush power steering. Use a turkey baster and suck out all the old PS fluid from reservoir. Refill with new. Repeat after a couple days of driving. Also look at replacing your accessory belt. Make sure not to over-tighten the belt. Squealing could also just be belt slippage from worn belt.
Plugs for your 96 will be the same as for an 02 wrx.
Thermostat will also be from an 02 wrx.
Radiator is from an 94 legacy turbo but without the trany cooler (try a legacy racing radiator).
Radcap is the same as a 02 wrx.
Rad hoses are different.
Fuel pump from/for an 02 wrx will work (such as a walbro 255lph).
Fuel filter from an 02 wrx will work.
Oil filter from an 02 wrx will work.
Water pump will be differient unless you have the oil/water heat exchanger.
Fuel pressure regulator from an 02 wrx will work.