Imo it's best to look at the engine spec first to determine the engines health, milliage etc, for example if it still has it's original head gasket which is a weak point.

Yes stage 1 is just a remap essentially along with a higher boost pressure.

You can do it DIY, but it's not just a case of 'plug and play' as many think!

Take it to a tuner if you do to get your AFR, ignition etc checked.

Martin