Voldemort's plan was more complex than his 7 creations.
The Horcruxes were designed to be found. They were designed to be interacted with in order for the fragment of Voldemort's soul to eventually possess the host.
The broad strokes of the main story for Harry Potter is that Voldemort created 7 Horcruxes with the intention of becoming immortal.
There is evidence that all of the Horcruxes were hidden with additional curses designed to weaken but not immediately kill whoever found them.
It is widely held belief that the potion that revealed the locket was designed to keep the person alive in order to be questioned. This makes the Horcruxes seem more like puzzles than actually hiding places. It would be easier to just make a Horcrux out of a meaningless object and hide it. Making Horcruxes out of meaningful items is just a trail of breadcrumbs. A trail that can only be successfully navigated by a incredibly powerful wizard.
All of the Horcruxes are designed to be kept and interacted with. We have multiple examples that the Horcruxes when worn have a significant impact on those that wear them. The locket is almost unbearable and the burden is shared between the trio. The ring begins to kill the person who puts it on. We don't see the final act of what ultimately would happen if the Horcruxes were allowed to continue unimpeded. The closest we get is the diary. The diary almost successfully reincarnates Voldemort but is stopped at the last moment by Harry. Why would only the diary have this ability?
This makes the ring Horcruxe all the more sinister. Voldemort wanted all the Horcruxes to be found by powerful wizards, but he wanted Dumbeldore to find the ring. Voldemort knew Dumbeldore would not be able to resist the possibility of resurrecting his sister. Voldemort barely hid the ring. The ring was just in a shak that could be fairly easy to track back to Voldemort.
The final two Horcruxes break the pattern. Nagini is not something a wizard would interact with. Nagini is something that can go out and FIND a host. In the event nobody finds any of your Horcruxes you have a giant magical snake that can hunt down a host crush them to a weakend state and involuntarily allow proximity to initiate the transfer of the soul fragment.
The last one as we all know was created by accident. IYKYK.
The Horcruxes tied Voldemort to the physical world but also had a built in mechanism to enable him to possess the wizard strong enough to find them. If that failed Nagini could force the issue as a failsafe.
Edit: had a fun idea. What if Horcruxes #6 and #7 were supposed to be the basilisk and sword of Godrick Grifindor?
We know Voldemort was obsessed with Hogwarts. He wanted something from every other founder.
What better Horcruxe that an incredibly dangerous nearly immortal serpent that you and a handful of others can communicate with. A serpent that just so happens to have a emense secret network of secret passages throughout the castle you intend to conquer and claim as you base of operations.