Do not whatever you do buy an oil filter for an S14.
Redtop & blacktop straight cam S13/180sx SR20DET's use the same oil filter.
This is what you want,
http://www.ebay.co.uk/itm/OE-Spec-Oi...MAAOSw2s1UwoJv
Absolutely no need to get the K&N one as it doesn't do anything extra.
The air filter is fine. Plugs, well personally if its standard I would run BKR6's not 7's. You should stick to 6's below 1 bar of boost really from experience.
Oil is personal preference, I use FUCHS Titan SuperSyn 5w 40 in my PS13, because it is or at least was one of the most cost effective fully synthetic oils.