It's an EJ25 right? I'm not sure why folks think it's an Ej22, am I missing something?
should make sure it's not valve covers or oil cooler (though that's only on passengers side if it even has one), cam seals, crank seal, etc. we can't see what's going on underneath/up front.
separator plate is on passengers side and doesn't usually migrate "forward" in the engine compartment, and the head looks wetter than the flywheel area/mating surface, so I'm hesitant to call that a separator leak. Of course hard to tell without more info/pic's/not knowing more, like if it was wiped off/cleaned.
1. The external oil leaks get worse very slowly, although 05+ models get worse quicker. if it's an 00-04 SOHC EJ25, with original gaskets, that hasn't been overheated before, and this is the start of a leak with no appreciable loss between oil changes - you can drive it probably 50,000 miles with leaking headgaskets as long as you keep oil in it.
all that to say - you've got lots of time on those engines.
the 05+ models get worse quicker.
2. Probably best to just replace them while the car is down, be nice to be once and done for good.
3. They are easily done in the car. Just jack the engine up a few inches in place and they're easily done in the vehicle if you want. Nicer to work out of the car.
4. Resurface the heads (no point in checking them for pressure or cracks or warapge - they never do that so don't waste time/money). there's a thread on here how to resurface yourself, very easy to do.
5. Use Six Star, Cometic, or Subaru headgaskets
6. install a Gates timing belt kit from Amazon for $120 and you're done for 100,000 miles.
you can even bolt the engine and trans together and install them as a lump all at one time if you have an engine lift. got to get the angle right and all of course.