How does that gasket have "better specs than OEM"? Don't fall for advertising guff, OEM is best on a stockish motor. The stock head gasket IS multi-layered steel (MLS) too. Doubling up on the gasket will drop your compression too (and thus HP) by a noticeable amount, not worth it.
I get all my gaskets and the like from Honda in Japan via JP-Carparts.com. Huge savings over buying from the local Honda ripoff merchants and you're still buying OEM quality. Anything not critical to the motor not exploding I get through Rockauto.com. I've just put a new valve cover gasket kit, cam plug, dizzy o-ring, sump gasket and oil cooler o-ring in mine to try and stop the rampant leaks that have developed. My valve stem seals aren't that old but they harden over time causing smoking, worth looking at if you don't know their condition. If I had to change my belt I'd be looking at doing the cam seals as well as the other stuff mentioned too. Are you planning on opening the motor (dropping the crank etc)? It's worth deciding where you are going to stop because a full rebuild might be unnecessary and extremely costly, but the bits I mentioned will all start to leak sooner rather than later on a 15+ year old motor.
Don't cheap out on the timing belt, if it goes then the engine is toast. 43,000km is close to half of the life of a belt, sooner if you trash it. Do you want to take the risk over a $100 belt? You can pick up a gates racing one for under $200 and be all racecar and shit. The auto-tensioner on these things is renowned for failure too. For the extra little bit of expense and trouble if changing the belt it's worth looking at a manual one. There is either the Kaizenspeed one which is kind of pricey but is a direct swap over for the auto one, or
this kit which is cheaper and replaces the pulley and whatnot too but is a little bit more work.