Well it totally depends on how well the prep work was done on the head/block surfaces prior to putting the gasket it. It also depends on the torque of the head bolts.
I remember you told me Metro Toyota replaced the head gasket, so ARP hardware was not used, although it should be torqued to 72ftlbs according to Toyota's new spec.
I can't tell you exactly how long its going to last, as I did not see the mating surfaces prior to installation.
For mods: None, until your car is in great running condition. You'll resent it know but thank us later.
Don't do what I did and get rod knock, I should have replaced my leaking seals sooner. Check your engine for worn parts (eg hard/cracked hoses, broken BOV, and general signs of age) and replace as necessary. I would also recommend going ahead and checking your valve lash etc, and maybe changing your timing belt if you do not know when it was done last.