Horcruxes... (!!!)SPOILER FOR THE END OF BOOK 7!!!

The way I pictured this horcrux thing working was this: Voldemort dies (if he really did die. Many people - like Dumbledore and Hagrid - believed that he was extremely weak and in hiding) and uses a horcrux to return to life. That bit of soul stays in him.

Going on that logic, the actual horcrux itself (the object the soul was placed in) would no longer "work" или need to be destroyed, because it wasn't holding anything.

No, he came back to life using his one last piece of his soul that was inside of him because his other Horcruxes still kept that one piece of soul alive. (and by the way, it was Crabbe who started the FiendFyre)

I don't really think it's 'used one up,' if you're talking about The Dark Lord. If Ты are talking about the The Leaky Cauldron barman Tom, I am afraid I can't help you.
Back on The Dark Lord, remember he was attached to Quirrel's head, right? He had no body, and was just a shadow. I don't know how he could have gone back to his body without using the old evil spell he did. He never used his Horcrux then, like put one in the cauldron so he could come back to his own body.
Also, The Dark Lord didn't die the night Lily and James did. The сказал(-а) later on that he was 'the meanest shadow, less formed that a ghost, yet still alive.'

He didn't have to "use one up", because he wasn't missing a soul after that night in 1981...he was missing just a body to put that 7th piece of soul to (the 8th - Nagini didn't exist by then). Because all other pieces were save in horcruxes (which are practically alternate bodies), when he got his own body back, the last piece of his soul was again in his renaissant body.

I dont really think Ты could "use one up" but if he did, it wouldve been the last part of his soul inside him...

I don't think the Horcruxes are "used up" when they're used. When the curse backfired when Harry was a baby, it killed Voldemort's body and released the fragment of soul left in his body. Because of the Horcruxes, that fragment didn't Переместить onto any afterlife. Instead, it hung around, hiding in Albania, and was the part of Voldemort which possessed Quirrell and was eventually placed into a new body by the potion Pettigrew made.