Well Orochimaru can supress his chakra, so byakugan nor sharigan would have noticed it...

And for the Village thing if you have a good status and alot of followers, sure try make your own hidden village, why not? Conquer a piece of land stay control of it and build your own village.

But Sound Village isn't a "Official" Hidden Village since Orochimaru hasnt gotten Kage status yet, i think all the other Kage's have to agree with it. something like that. This part is debateble since they never really explained how to achieve all this.

It may be pretty clear by now Orochimaru is feared and very powerfull. If he wasn't that strong Hokage would already commanded all the Jounins from Konoha to kill him, but he didn't, cause he knows Oro will pwn the crap out of Konoha.