As many have mentioned, start with the easy gains:
Fastest tyres (GP5000 rear and Aero 111 front)
Tight clothes
Aero socks
Aero helmet (Evade)
Overshoes
Bikefit (!)
Narrow handlebars (36-38cm)
Aero handlebars
Of course wheels are more fun, but starting with the above makes a big difference.
And if you were to get a pair, I’d recommend something that is modern and wide, if possible. Such as the Reserve wheels or similar.