Lovely car ! Nice to see a clean example. As for upgrades, a plenum spacer (i think anything over 5/16'' wont fit under the factory strut bar), high flow cats (im sure decats will do the same if not better), and a drop in filter all with a tune from horsham has got my car to 285bhp for reference, so around 9bhp increase from factory new standard and this is the increase ive been seeing on most zs with the general bolt ons, some with a little more. Ive hardly ever heard anybody mention throttle body spacers on really any platform at all.
Seen them discussed here and I think the verdict was it'll not do much ? Could be worth a go ive got no idea 🤷♂️
I have not had brain surgery (its stock so far) so cannot talk on the bhp gains from that.
As for confidently over 300bhp im not 100% sure itll be pushing that but what do i know. Enjoy your new car !