Abnormally

His unique character quirk. ( will be explained in the future )

I try not to use 'heavy' swear words, so I'm stuck with this :0

Maybe, Perhaps, Mayhaps

If such artifacts exist, yes.

Vanish doesn't require mana ( It's his character quirk )

will never.

Unfortunately, he can't use 'that' Mana to cast spells as it requires the mana to travel through his body to 'conjure a spell' and since he does have a terminal illness, his body is unable to support this mana 'journey' through his body ( you can think of it as if his meridians responsible for storing and moving mana are ripped apart ) So apart from casting spells he can try to interact with mana outside his body, but again, he has no experience nor clue how to do it as he was always Manaless.

Mana illness will not be healed in the near future, maybe even forever ( hadn't planned that far ahead ). Using mana stored in an Artifact/some kind of storage is definitely available.

I wasn't.

Kinda? I've taken the main ability of its MC and then removed some of the restrains it had. Basically Yoink and Twist method. But the story is completely orginal dw.