“4) There were a bunch of suggestions but I don’t think any of them really addressed the question. I was not suggesting that Harry shouldn’t have been involved; he should have been able to get help (from a minimal amount of people).”
I believe sirvoddmort answered this satisfactorily.
“The plan had to be confined to a small group, because were it to be revealed, Voldermort could easily foil the plans. This explains why Harry (who we already have proven must be an integral part of the plan), could not enlist the entire Order to help destroy Horcruxes, as it would mean that only one person had to be broken for the plan to fail.”