No, he obviously doesn't need Susano to use the items. But that is besides the point. The reason why Black Zetsu exclaimed that Itachi is invincible is because of the combination of Susano + Yata Mirror + Totsuka Blade. Not just because Itachi possesses them. He didn't state that the items are invincible.
We also don't know how much chakra wielding these items exhaust without a medium like Susano'o. The event of Itachi using these items without Susano was never introduced, so the point you're trying to make is more or less non-sequitur.
Yata Mirror is also not ninjutsu; it's a spiritual weapon.
Hmmmm, that's true. You could be right there. The only time Itachi has used Totsuka Blade without Susano'o was when he was an Edo. But if Orochimaru wanted to use it, could it really exhaust that much chakra? At the same time, I agree with what you're saying. There really is no way to know at all how much chakra is required to use the items.