HI induction kit, not rearly unless its a viper inclosed style one, would personally recomend drilled air box and a performance filter (i have my old drilled air box yours for the price of postage)
decat the second cat/the one below the gear lever, yes defently recomend doing it, one of the first mods i did, only other way to remove the pri cat/the one in the down pipe is to go for a hot shot header from the states (ebay) would also recomend if your changing the manifold to go for a full stainless exhaust system.
handling, cant go far wrong with coil overs but there not exactly cheap, for a cheaper option go for a set of PI springs had them on my car for about 60000 miles and took a hel of a lot of abuse including the almera towing car trailers with vectras and the likes lol.
hope this is some help