Hello and welcome. There have been a few talking about a turbo on the z22se but it has never come to anything yet.
The mods that you've have carried out so far are a good starting point. I would say that you may be producing around 155/160bhp going on my experience. The induction kits are a little frowned upon when used on the z22se due to the large amount of heat under the bonnet. The majority keep the standard airbox with an upgrased panel filter such as K&N. Then they change the induction pipe to the throttle body for a Vectra C induction pipe or some have bought the aluminium pipe with silicone joints/elbows so that you get a larger bore pipe to the T/B.
A modified cylinder head and a set of cams can help things. Also a good addition is a 2.5 inch custom downpipe including 200cpi sport cat. A piper 4-1 S/S Manifold is another good mod. It really all depends on your wallet size. The ultimate fo rthe z22se is the Supercharger conversion available from Courtenay Sport. These conversions come in Stage 1, Stage 2 and Stage 3 now. Stage 1 is good for around 210/220bhp. Stage 2 is good upto 250/264bhp. Stage 3 including upgraded rods etc is good for 300bhp. You can further enhance this by adding forged pistons, different pulley and its 300bhp+. There is also a Harrop Supercharger that is available that's being fitted to a vx220 which will be an absolute monster.
Stage 1 comes in at about £3500. Stage 2 at about £6000 and i'm not sure on the cost for a Stage 3.
There is also a throttle bodies option that a member on here (Vocky) has set up on his vx220. Very lovely sound with a punch to match. He can advise you more on that.
Welcome to tuning!!
;-)