I'd be interested to see what their explanation for how the FTL works is going to be. Even if it is slower than the "hyperspace travel" that they made up for SG1 and atlantis, it is still many times faster than the speed of light and therefore must utilize some sort of space manipulating type of drive. The idea of "FTL engines" doesn't make sense, since that would seem to indicate that it is actually being propelled in a more conventional way at those speeds, which is impossible.
It's FTL but not hyperspace. That's all you need to know. In-universe, there have already been multiple ways to go FTL: by Stargate, by hyperdrive and by wormhole drive. Destiny's FTL is just one more type.
Compare to Star Trek: There's warp drive, transwarp, quantum slipstream, subspace corridor, wormhole, power of Q and problably a few more I've forgotten.
What do you mean that the 8 chevron gates were a "visual effects error?" It sounds to me like they didn't know that they were going to need them to have 9 chevrons for a future spinoff. There aren't "errors" that somehow remove of a specific entity from a rendering... If they space gates had 8 chevrons, then they put 8 chevrons on them.
Go back and re-read what I said. There have always been 9 chevrons on the Stargate, as far back as SG-1. The physical Stargate model that you see at the SGC has 9 chevrons, two of them are simply blocked from view by the ramp. If you watch SG-1 Season 4's Exodus, you can barely make out all 9 chevrons in the scene where the gate is tossed into a sun:
http://www.stargatecaps.com/sg1/s4/422/html/4x22_219.html
It's hard to see but the 9th chevron is at the bottom left.
As for the CG error:
This gate, with 9 chevrons, is from Rising, Part 2, i.e. the first episode of Atlantis:
http://www.gateworld.net/gallery/displayimage.php?pos=-196848
This gate with 8 chevrons, is from The Return, Part 1, a 3rd season episode:
http://www.stargatecaps.com/sga/s3/310/html/return1_0080.html
Note that there are 9 chevrons in Rising and 8 chevrons in The Return
and Rising aired a full 3 years before The Return.
Errors crop up in visual effects all the time. It could have been done for cinematic purposes to make the gate look symmetrical with all chevrons lit, or it could have been a slip up in digital asset management. Like some intern accidentally overwriting different versions of a model. There's also the issue of having more than one production company working on visual effects. One may have erroneously created an 8 chevron gate.
Also, if this gate and ship is much older than the atlantis and SG1 gates, then why is it so much cooler? A gate that completely spins is way cooler than a gate that only partially spins, or doesn't spin at all...
My 1974 ITT Model 500 rotary phone has a spinning dial. My 2005 LG cell phone does not. Which one is newer?
How did they cope in Star Wars? A Clone War that wiped out the coolest technology?
None of the technology seen in the Episodes I - III is objectively any better than that seen in the Original Trilogy. The starships are smaller and less powerful. Blasters and lightsabers are exactly the same. The Original Trilogy had two Death Stars which are orders of magnitude more powerful than anything seen in I - III.