Chinese: 我 VS 本人?

In most situations, nope, in few situations, yes.
Though the outward meaning of “我” and “本人” is same, the immediate feeling of the listener and the mindset of the speaker is not same.
“本人” is a formal(serious) term normally used in letters written to Governments, or someone you want to sue him.
In daily conversation, E-mails, giving a speech, you use “我”. Even in the situation of a quarrel, I think to use “我” is enough. And, yes, someone might use “本人” to emphasize his disappointment.
When in a daily speaking, if you say “本人”, you just make a disharmony between you and the person you are talking to.
When you put ads on somewhere to sell your house, etc., then, it’s interchangeable between “本人” and “我”.

Nope, it seems 本人 can only be used when the subject has already been established or is understood from context--it is simply a reflexive pronoun--ex. he/himself, me myself, you yourself etc.

They can also be used together, ex.:
wo ben ren mei jian-guo (I myself have never seen it/ I've never seen it myself).

It seems "本人" is rarely used in the objective position.

Also, it seems "本人" is used for emphasis, reiteration or clarification.