there are arnt many flywheels out there that are 'too' light, what you get is a loss of revs up hill with constant throttle position.....you wont notice this with a lighter one. id be suprised if you could find one that made this much difference tbh

you will need the 2l managment, cams and MAF to make the most of the engine too, and once you have the 2l managment theres no problem if you decide to put a 2l bottom end on....

the inlet of the 1.8 just squeezes in i beleive, the 2l wont fit.

as for manifolds, ashley are good but arnt stainless steel, you can get kits to make your own if your up for a bit of a challenge but most aftermarket ones are good, just try to make sure the headers are of as equal length as possible