toyota reccomends double tip plugs? where'd you get that info? if that is true, that would be interesting as i've never read or heard that. as for my comment on iridiums, the 1sz-fe is an economy engine and at most you'll get 0-1hp increase, which is not worth the extra cost unless you fit spark amplification (Like MSD).
the size i suggested will keep your meter accurate etc. if you want to fit oversized tyres all i can say is good luck. as for the oil filter, the same filter is used for the SZ, NZ & ZZ engines according to the box.
no luck yet on the owners manual (N), as for the oil filter don't buy the guard one, skullbox did and it leaked in 10 minutes, spend 350 and get the original one. shell yellow is just fine as long as it is original.