The second gen Legacy ("first gen" Outback) is a pretty easy car to work on. At this generation basically everything still interchanges with the Impreza, boneyard parts are common, and it doesn't have a lot of the "luxury car!!!" trim pieces that they added on the 3rd gen that break and annoy you (like the butterfly-opening cup holder). I think they're more fun to drive than the tubbier third gen as well.
98 means it should have a DOHC ("Phase 1") 2.5L; these ones, as Furious_E said, have internal head gasket leaks. Usually they've been overheated a few times as a result, which isn't really great considering they're aluminum engines with a short crankshaft. If you do the head gaskets also budget for everything else you usually replace when an engine has been overheated; hopefully it was parked when it started and it wasn't daily driven while overheating like many of the head-gasket Phase 1s I've seen for sale.
If you're planning on this being a "forever car" and send the engine to a machine shop, make sure they use an appropriate torque plate. You can pick them up for an integer multiple of the price of another used engine from a place like Company23. In your shoes I would probably just replace overheating-vulnerable components, fresh head gaskets, redo the timing belt and friends (idlers, tensioners, water pump) and beat on the car like it owed me money, which it would.
Replacing the gaskets themselves aren't hard; I would yank the motor and do it on a stand, but on these cars you could probably do it in the engine bay if you really like taking 10x as long. Plus, yanking the motor will let you replace the rear oil separator plate.
SOHC ("Phase 2") EJ25s usually just leak externally, so you can keep tooling around like normal and just top up the coolant and oil when it gets low. I'm embarrassed to say how long my daily driver has been in this status.
If you buy the Outback and replace the head gaskets, make sure to get steel/MLS 96-99 Phase 1 turbo gaskets to replace them. The dealership will give you more crappy stock gaskets if you come in with your VIN:
if your phase 1 2.5 needs headgaskets get 11044AA610
if your phase II 2.5 needs headgaskets MAKE SURE to get 11044AA642. The dealership will not give you these gaskets if you give them your vin.
If the EJ25 is pooched, one option which I like quite a bit is that the Phase 1 EJ25 and the Phase 1 EJ22 basically share their intake manifold, electronics, etc so you can bolt in a stone-reliable EJ22 in lieu of the EJ25 and give up about 25 horsepower in exchange for never having to worry about head gaskets ever again. They also fit the character of the car a little better (the EJ22 is the greatest tractor engine ever made).
Honestly that picture looks so nice I would already have bought it and put head gaskets or an EJ22 in.