They're a solid platform. Interference engine so I'd immediately be installing all new Subaru or Aisin timing belt, tensionser, pulleys, and water pump if it's in good enough condition to warrant that. You don't really want a 25 year old lower cogged idler - they are by far the most failure prone item on there.
If minimalist is preferred: replace the timing belt and lower cogged idler - those are the two parts most likely to fail. The others don't fail often anyway and often times give you warnings the others don't. After market belts and pulleys aren't as good, I've seen the pulleys fail and the included tensioner bolts shear.
While you're in there it's not a bad idea to reseal the oil pump (anaerobic sealant, one o-ring, and the crank seal) and tighten the backing plate screws - more than one are always loose.