The head gaskets last seemingly forever if the engine never overheats...unlike some cars where they'll simply fail all on their own anyway...but yeah, a lot of guys with even a single overheating lost the gasket...
the service manual is stickied at the top of the protege forums...you'll find it. The job is a lot easier than some other cars, but still takes patience and at least a full day to put into it...Ideally you should have cylinder head checked, overheating can cause it to warp slightly and no longer be square...which will cause the new gasket to pre-maturely fail...most shops can check that very quickly if you take it in off the car, and for nearly free...you can also do it yourself, but it would take some pretty precise measurements...if it needs adjustment, they'll machine it down to square again...and you use a slightly thicker head gasket to keep compression the same...so if you are doing it right, its a good idea to have the head checked BEFORE you order the gasket...in case you end up needing an over-sized piece...
might as well replace the timing belt, tensioner, intake manifold gasket, exhaust manifold gasket, and valve cover gasket...as well as check valve clearance while you're at it...you have to get into all these areas anyway...
lastly...a lot of guys go with ARP head studs to finish the repair...its ill-advised to reuse the stock head bolts after its overheated...and the dealership cost is nearly as high as aftermarket studs...which are much stronger...
