Instead of destabilizing the elemental nations through warfare (by invading Konoha), Orochimaru decides to do it economically by using Edo Tensei for cheap slave labor. And not just by renting out S-rank ninja zombies at prices even Akatsuki can't compete with; he also revives famous inventors to run his R&D departments, charismatic leaders to work public relations, talented engineers for skilled labor, etc. Basically he creates an undead megacorp filled with the best and brightest of human history, none of which require any compensation or upkeep, and all of whom are utterly obedient to him while mostly retaining access to all of their memories and personalities.
I mean really, it would be much easier and more productive than creating a zombie army. No one would be able to fairly compete with his zombie corporation.