“...I am thinking 1K rounds of ammo should be enough ...”
You need a bit more than a thousand rounds, friend...
And it won’t only be the hordes from the city you need worry about; it’ll be FedZilla and thugs with badges that consider you a threat for having the temerity to believe you actually have rights and property worth defending.
If Fedzilla comes after you, no amount of ammo is going to do you any good.
You’re facing a practical infinite foe there.
The only way to take on that monsters is to nip at his heals from concealment.