I'm probably re-iterating other's points here, but if you want to stick with the CA20 in NA form, get it to breathe. And it all depends on how much you want to spend.
- start with bolt ons; big free flowing intake with a cold air box, preferable sealed, and with its feed coming from the front bar so you get a ram-air effect at speed. A decent size exhaust and cat will help, i'd go for a 2.5" cat back with mandrel bends, and a metal cat with 2.5" outlet and a 2.25" inlet, build a set a good 4-1 extractors for it.
- get a stock inlet manifold, cut it down, and weld on a new plenum, that is significantly larger in volume (ie greater than 2.5L, on a 2.0L engine i'd go for around 3-3.5L plenum) with the entrance to the runners from the plenum being bellmouths. For throttle bodies, go for a single KA TB or try and pick up a twin throttle body from a mustang/RX7/cadillac catera.
- get someone to port the head and do a 3 angle valve job; run a BIG cam in it too.
- with engine internals, get the lightest pistons you can; ACL's hypereutectic pistons are lighter than stock cast pistons, and if you get them in 1mm oversize, that should bring your engine's size upto approx 2.1L.
You can spend as much or as little as you like; IMHO if i were in your shoes wanting an NA build i'd start with a KA24DE or SR20VE due to the aftermarket parts available for them.
Me, personally, i'd be doing a KA24E NA build, but that is because i am a little nuts.