We note in Deathly Hallows that there already seems to be an antipathy between the sword and the Horcruxes.
Dumbledore was probably taking the precaution of not taking a powerful magical artifact to a location where setting off any kind of alarm could cause the operation to go pear-shaped.
It may not be the Dark Lord’s unique curse.
Though the Dark Lord does invent spells, there’s nothing that says that specific curse is unique to him. He also uses more well-known Dark magic that other wizards can cast as well, like the Unforgivable Curses, which predate him by centuries.
“19 The Cruciatus, Imperius, and Avada Kedavra curses were first ...
Voldemort never knew Dumbledore found his Horcrux
The last time Voldemort saw Dumbledore was when he dueled him in the Ministry of Magic, at the end of Book 5. Dumbledore acquired the Resurrection Stone/Marvolo Gaunt's ring some time in between the end of The Order of the Phoenix and the beginning of The Half-Blood Prince. Remember that Harry saw Dumbledore'...
He looked like he did when he was ‘reborn’.
Though the Dark Lord isn’t explicitly described on the night he kills the Potters his appearance is unusual enough to scare a Muggle child, and further, from Harry’s nightmares of that night that it was the same as when he was returned to a body.
“Nice costume, Mister!’
He saw the small boy’s smile falter ...
It’d open the Chamber to prove him as heir.
Tom Riddle planned that his diary, after being made a Horcrux, would be used to reopen the Chamber of Secrets someday. That would then show that he’s the heir, since the legend of the Chamber says that only the Heir of Slytherin can open it.
“The story goes that Slytherin had built a hidden chamber in the ...
The diary does not prove that he is heir of Slytherin.
The fact the he can talk to and control the Basilisk proves that he is heir of Slytherin.
The diary originally probably contained his notes about how he found out that he was not a muggleborn orphan, but a descendant of that Gaunts and of Slytherin, and how he found clues in the castle about the ...