Because this is in the present tense. wird is not being used as the modal verb will here as there is no infinitive at the end of the sentence.
Depending on context, yes it could. Without further context, I'd say 'addicted' is the better choice.
I don't think you can just write Mann wird. It would need to be preceded by der or ein.
"One will become addicted" means "Man wird abhängig werden". It is a bit complicated.