Don’t get a gun in some obscure caliber. Get a pistol in 9mm or a riffle in 223 (even better get a 5.56x45 NATO) or 308 win, that way ammo will be cheaper and you can better afford training with it. Shooting a few hundred rounds is not really enough. You’ll need to train regularly.
Learn how to maintain your gun. As in how to clean it, what parts need lubrication, adjusting the sights, etc.
Speaking as an electronic engineer, get passive ear protection. Active noise cancelling is cool and all, but what about when the batteries run out and you have no protection? Or what the electronics fail? Protect your ears, but when you can get +100 rounds of ammo for the price difference, then I would prioritize the ammo budget.
Whenever this comes up I like to add: