Alright, let's do this:
Dooku was on a powerful dark side nexus. Relevant quotes:
First of all, your first two quotes are Obi and Anakin's opinions based on the legends they've heard of Korriban. To quote:
"Anakin felt the dread in the room. He knew of Korriban only through legends."
"'The Valley of the Dark Lords,' Obi-Wan said. They had heard of the valley from their earliest days as students at the Temple, had used tales of the valley to scare each other as younglings."
-- Final Showdown
Your other two quotes seem to be more the Dark Side calling to the Jedi, tempting them, more than hindering them. The quotes suggest as much:
"He felt it now, the dark side of the Force emanating from the planet's surface. Looking at the faces of the Jedi, he knew they felt it as well. It had a sick sweetness to it, something that seemed to pour through his veins, attracting and repelling him at once. It was the most complicated surge of the dark side he had ever felt."
-- Final Showdown
"He began to pick up a whisper. Then another. He couldn't make out the words, only the intent. Someone was baiting him, cajoling him, laughing at him... or was it his imagination? Was it just the wind whispering through the stones?"
-- Final Showdown
This doesn't really speak to the nexuses potency, since something very similar happened to the subdued nexus of Ambria during Nomi's training there:
As Thon says, that's the Dark Side tempting the Jedi, testing them, challenging them:
Heck, it might've even been the spirits that opressed Palpatine when he went to Korriban:
The quotes about the valley are valid, but all that really confirms is that the place was a DS nexus, which we already knew. But to what degree? How potent was it? Nothing in the book notes that, to my memory, but Path of Destruction does:
"A chill wind blew across the landing pad as he disembarked, but it didn’t bother Des. After the stale air of the pit, any breeze felt good. He felt a shiver go down his spine as his foot touched Korriban's surface. He'd heard that this had once been a place of great power, though now only the merest shadows remained."
[...]
"Still, he was troubled. He remembered the first time he'd set foot on Korriban. He’d sensed the power of the world: Korriban was alive with the dark side. Yet the feeling had been faint and distant."
"When he’d left the temple and the starport behind, he’d expected that feeling to grow stronger. With each step drawing him closer to the Valley of the Dark Lords he thought he'd feel the dark side growing in its intensity.
Instead he'd felt nothing. No noticeable change at all. He was only a few kilometers away from the valley's entrance; he could see the shaded outlines of the nearest tombs carved from the stone walls. And still the dark side was no stronger than a hollow echo, no more than the lingering memory of distant words spoken in the distant past.
-- Path of Destruction
And keep in mind that Korriban's nexus was continuously weakening according to Palpatine, for seven thousand years:
"Korriban has lost potency over the past 7000 years, but it still whispers of dark secrets."
-- Book of the Sith: Secrets of the Dark Side
So the Dark Side was just tempting the Jedi in question, and Dooku was only amplified by less than "a hollow echo of distant words spoken in the past". It goes without saying that the amp would be all but negligable.
The vehicles were described as "corroded", so it's likely that time and/or the Dark Side allowed them to waste away, meaning less mass and weight, and all of the ships were regarded as "ancient", meaning the corrosive wreck of a ship Dooku pushed was likely falling to bits...
Many of the cruisers are described as a "wreck":
That's fair, age has definitely taken it's toll on the ships.
[B]He didn't throw anything other than small pieces of smashed up vehicles - the text explicitly notes he pushed the cruiser across the ground. He didn't throw it.
Eh? He didn't throw smashed up pieces, lmao. He threw the entire vehicles, and nothing in the text notes the cruiser was pushed across the ground, it's just noted as zooming towards them, i.e. moving quickly.
Nor is it said anywhere about the specific size of the cruiser - but it can't be all that large, given that it's wings were shorter than Obi-Wan, forcing him to duck under them so he wouldn't be hit by them. Regarding Obi-Wan's cruiser earlier in the novel, the only relevant size measure I got was that it was small, and was only intended to hold two individuals - this is the author's idea of what a cruiser would be. Obi-Wan muses that Anakin and Fetus would be cramped together in one:
You're confusing two vehicles, 'Swords. Or maybe you forgot to emphasize a certain part of your quote:
"[He flattened himself against the wall as another vehicle moved, its jagged wing a lethal weapon, capable of slicing them to ribbons. A cruiser suddenly zoomed toward the wall, straight at them.
"Drop!" Anakin and Obi-Wan hit the floor, hugging the stones as the cruiser passed over them and smashed into the wall."
-- Final Showdown
If you read the qutoe in it's entirety you'd realize the vehicle that could've sliced Obi with it's jagged wings was already avoided when Kenobi "flattened himself against the wall". Next the wording "a cruiser suddenly zoomed toward the wall" implies it's a separate vehicle for two reasons:
1. If it's the same vehicle with the jagged wings as before, it would've been referred to as the cruiser, that's just basic English grammar.
2. It wouldn't have suddenly zoomed, as it was already moving.
The text simply doesn't align with it being the same vehicle. And before you say how Anakin and Obi-Wan ducked under it, I'd argue that's because the cruiser was thrown, thus it would've left room underneath it to duck under.
Next, the word cruiser itself is used very loosely in the novel, anything from a speeder to a warship can be deemed a "cruiser"(also, Obi's commentary is purely due to Anakin's and Ferus' rivalry, otherwise the cruiser itself has held several Jedi within it). So that makes it even vaguer to determine how big they are, but we know they're large, hulking, giant phantoms. They're meant to be massive. Most Ancient Sith Warships are incredibly large, given just their pods can hold within them two Sith Behemoths(which are, on average, at least 12 meters tall and 6 meters long):