Yeah, but then where does his body surf ability come from in Legacy? He can do it to Janeka/Larius, the dragon was nowhere to be seen, and he'd yet to acquire the orb that supposedly gives him control over the dragon.
Maybe the dragon serves as a sort of signal amplifier instead of being the source of the body surf. So for example, he can body surf to Janeka/Larius because they're RIGHT FREAKING THERE. Bianca gave the location of the primeval thaig to a Warden who was definitely possessed by Cory, but didn't look like him. So maybe the red lyrium dragon lets him surf greater distances and immediately change the host into his form. It basically supercharges the ability. Then at the end, when the dragon dies, there's a feedback thing like what happened with Saren and Sovereign that temporarily shuts down his ability to surf.
Or maybe I'm just reading too much into a plot hole 
Yeah, but then where does his body surf ability come from in Legacy? He can do it to Janeka/Larius, the dragon was nowhere to be seen, and he'd yet to acquire the orb that supposedly gives him control over the dragon.
Maybe the dragon serves as a sort of signal amplifier instead of being the source of the body surf. So for example, he can body surf to Janeka/Larius because they're RIGHT FREAKING THERE. Bianca gave the location of the primeval thaig to a Warden who was definitely possessed by Cory, but didn't look like him. So maybe the red lyrium dragon lets him surf greater distances and immediately change the host into his form. It basically supercharges the ability. Then at the end, when the dragon dies, there's a feedback thing like what happened with Saren and Sovereign that temporarily shuts down his ability to surf.
Or maybe I'm just reading too much into a plot hole 
Yeah, I think so too. Isn't there some mention of the dragon amplifying his ability?
I imagine that the Magisters and the Archdemons both have the body-surfing ability, it's just that the Magisters can even do it to ghouls like Wardens.
As for Witcher 1: I'm torn. Witcher 1 introduces you to Geralt and company, as well as many of the movers and shakers of the storyline, gives you your first brush-up against the Wild Hunt (Who are discussed a lot but do not appear in 2), gives you lots of hints at Geralt's past that come up again in 2, and let's you know the general themes, monsters, and kingdoms involved. Also, you get to know the other Witchers of Kaer Morhen, who again, show up later, but not in 2. There's the Full Combat Rebalance mod if you decide 1's combat is too clunky and too easy. 
But Witcher 2 is the bomb.com.
And, while many of the characters and Geralt's search for his memory plot carry over, the main plotline of 2 and 3 are largely unrelated.
But Witcher 1 has Thaler and Eredin.
I will admit that in 1, the Prologue and Chapter One are weak. Chapter Two is where it gets good. It's like when you are finally free to wander the galaxy in ME1.
If you're going to skip 1, look up a general sum-up of Witcher lore and characters, and then the final cinematic cutscene of 1, which segues directly into 2's plot. 