Assume we have a Wizard who is at least level 13 and can reliably cast Sequester many times (either through acquired spell scrolls, or has acquired enough material components for it to be a non-issue), has a safe place (through the spell Demiplane) to be under the influence of Sequester for many centuries, and has access to the Manual of Bodily Health, Manual of Gainful Exercise, Manual of Quickness of Action, Tome of Clear Thought, Tome of Leadership and Influence, and Tome of Understanding.
Per the item descriptions in the DMG:
…your [STAT] score increases by 2, as does your maximum for that score. The manual then loses its magic, but regains it in a century.
Now, normally this would be a once-in-a-lifetime use, or maybe twice (due to the lifespan of the races), but if a wizard used Sequester on themself, many years can pass without growing older:
…[willing target creature] falls into a state of suspended animation. Time ceases to flow for it, and it doesn't grow older. You can set a condition for the spell to end [before the spell is dispelled by the caster].
So, assuming that time continues to flow for the magic items, but not for the sequestered wizard, can they study these books and take the necessary long rests, Sequester for a hundred years, “wake” from the Sequester, and then repeat an arbitrary-but-finite number of times for an arbitrarily high (but finite) improvement to their stats?
To end the cycle and escape the demiplane, the wizard would simply Plane Shift out:
…You can specify a target destination in general terms … and you appear in or near that destination.
Best Answer
RAW allow it, but there are some setbacks.
Crawford also agrees (thanks to V2Blast for that).
While you have done an excellent work in tracing the requires rules and components to make all of this work, there are somethings you need to rethink.
3200 years is an immensely long time.
Consider that, every time the Wizard freezes himself in time in his dimension, the entire world ages a century. Civilizations rise and fall, continents change, plagues ravish, dragons destroy. Industrial revolutions rise, ice caps melt, Gods wage war upon each other. While your Wizard could ignore all of these, someone that didn't take a long time every century to follow up on all of these events would soon find themselves completely lost in the world, not knowing where to turn to anymore, and only imagining how the carriages without horses worked.
Learning all the books takes a long time every time, where food, water, safety, and above all sleep, are necessary.
The Wizard cannot just spend 300h studying books. By the 5th day, he'd die of exhaustion (seriously, by RAW, 5 levels of Exhaustion kills you!). He needs to rest everyday, to take care of his health, and would take a lot more time than the minimum you've allotted.
After a few centuries, the Wizard can barely describe a place to appear at.
Imagine he had a home to come back to. After a century, it's probably been taken over by some other resident. After another, maybe it's been abandoned. Another and it is now the home for devils and mindflayers. The nearest town has grown to a big empire. In another century, it has waged war and dwindled in size. In another, a plague has consumed anyone who was left there. As the world changes, the places the Wizard has to come back to all vanish. He can always come back with some general description, but he has no real place to come back, no place he can recognize. He stops knowing how the world behaves, he doesn't know what is dangerous anymore, and how to fight the new threats.
Does a sane man really want to throw everything away to become powerful?
Every story has a big villain. Some demon risen from Hell (Tarrasque), some alien from another planet (Megatron), some angel fallen from grace (Sauron). Your Wizard would become this villain. He attained immense power over the centuries but lost touch with the world. All he has is power and the strength to use it, but he isn't part of this world anymore. The new races who have emerged will barely recognize him. He cannot bond with anyone, as everyone is so dumb and boring compared to himself. He is, in all respects, a higher being. What does he want to do now? Control the world, for the greater good? Or destroy it?
How would the world see him?
A creature emerges out of thin air. Taller, stronger, grander than anything these primeval races have ever witnessed. The air around him fizzles with raw arcane powers. He speaks a forgotten language, no one comprehends it anymore. The crowd gathers in awe. A flash of flames appears, an exhibition of his skills, but most of the crowd looks scared, and starts moving away. This alien god looks angry at the lack of adoration by these puny creatures. In a swift gesture, all of them are incinerated. They will bow down to their new leader or perish. Accept this wicked salvation or be destroyed.
This is how villains are born.