absolutely go to josh's site and down load the 2000 FSM. you will be glad you did.
i don't recommend doing it in the car. i just did my first ''head gasket'' job and it was tedious on an engine stand. i cant imagine doing it in the car on a 2.5L engine. single or double cam does not matter. my .02 worth.
use ''subaru'' head gaskets, period. others may work fine, but you can get them online, both for about 75$ total plus shipping. others are not going to be dramatically cheaper. i use subau plug wires, and seals /gaskets for the cam, crank, oil pump o-ring (reseal it), and maybe the coolant crossover pipe o-rings, depending on the miles. everything else i use generic stuff from the parts store.
on my 01 HG job i spent $140 with a lacal dealer, wholesale (same as the online dealer cost) in subaru parts. i then spent about $250 for a timing belt kit (new belt and everything it touches, water pump, all idlers, and tensioner) on ebay, i use ''theimportexperts''. fluids and manifold gaskets, and NGK plugs i got from the local parts chain store.
also my opinion, if the engine has not over heated, you probably do not need to have the heads re-surfaced. (use the reverse torquing sequence to remove the heads) i did not send mine to the machine shop and mine runs great. i have heard that the some dealers don't even do it. if he engine runs good now, and you remove the head and re-install the head properly, it will run good when you are done.
FORGET top dead center. subaru almost NEVER uses it. they have adjusted all of the instructions for timing belt / head gasket work to be done with the pistons at mid stroke. use the FSM, or ask here, and set the crank to the timing alignment mark before you remove the belt. IT"S EASY.
use the hash marks , NEVER use the arrows. notice that the crank keyway is located down in the 6 o'clock position.
DO NOT remove the cam shafts. you do need to remove the cam sprockets to replace the seals, but not the shafts.
i would use a braker bar on the crank bolt BEFORE you pull the engine. put the trans in 1st and the hand brake on and have a friend stand on the brake pedal. or use the ''starter bump'' method. i have used a chain wrench and it works, but you run the risk of destroying the harmonic balancer. (your best bet is to use an impact wrench after you have pulled the engine, but they cost ~$50 at harbor freight). on reinstall, put the trans in gear and the hand brake on. (auto trans have a different procedure.)
TORQUE the crank bolt on re-assembly to 135 ft lbs. failure to do so and it will work loose over time causing trouble $$$.
no need to replace the head bolts. some folks insist that you must, but no where in the FSM does it say to replace them. be sure to coat the head bolt threads and washers with fresh motor oil at install. follow the torquing procedure very closely. you will need a torque wrench that goes down to 11 ft lbs.
good luck and stay in touch.