As inventor; is it necessary to be a bonafide "business" to approach interested capital investor(s) with a proposal of ROI agreement?

The term "bonafide business" has no meaning.

What do you mean "bonafide business?" Do you mean profit motive? Do you mean separate legal entity? Do you mean EIN applied for with the IRS? Do you mean registered with the Secretary of State?

A kid who has a lemonade stand in their front yard has a bona fide business.

So, the answer is, "Yes, you must have a bona fide business before you approach investors," whatever that means.

No.

Just make certain that anything you tell them is accurate.

The worst thing you can do in a situation like this is to misrepresent yourself.

Not necessary. It might give you more clout and make damn sure the invention is protected (patented, or whatever) but not necessary.