Vulcan, orbiting Eridani A, is one of a cluster of odd and barely M-class masses that can be inhabited...apparently.
So? Nothing about that gives Vulcan a moon.
Spock's statement was never meant to stand up to...anything, just make his world alien to ours.
Who says so? Just some Johnny-come-lately who didn't care about canon or who didn't bother to ask before diving in?
Motion Picture wanted EPIC and therefore gave it about 50 moons to look cool, the Directors Edition clouded the sky so we didn't see them.
50? My sources say 2 orbs – not moons – and considering this is a trinary system (one large star, one red dwarf, one white dwarf), and Vulcan apparently has since been given a sister planet (two planets orbiting each other, one with a moon, no less, but not Vulcan), all of that can be explained as something other than a moon.
Also changing Vulcan from having a dark amber sky, to no visible atmosphere (sort of) even in the day time, which changed to red in TOS-R, then beige smog in TMP, then blood red/orange in ENT, then just a freaking sky in 2009.
So, no weather where you're from? No dust storms, either? And with two other suns in the sky, which ones are up, and what light is shining through the atmosphere that day is just unknown since nobody is looking at that kind of detail.
From having no "moon" to several planets and moons nightmarishly close, to a sky where you couldn't notice, to having no visible orbiting partners from 2001-2009, then a sister planet nearby.
As stupid and as lazy I think those inclusions were, all could be and have been more or less reconciled with canon, and Vulcan still has no "moon." A sister planet with a moon, apparently, and Delta Vega (God, what a moronic choice for a name, particularly as it is not even a native Vulcan name for the place) possibly with a highly eccentric orbit that brings it close enough to Vulcan to see each other as discs in the sky, however rarely that configuration might occur, still doesn't violate canon. Spock did not say,
"Lt. Uhura, Vulcan has no moon, or a sister planet, or a nearly intersecting orbit with another planet that gets so close once every 237 years (or whatever) you might think it's a moon if you didn't know better, but Vulcan has no moon, I assure you. I'd know, as surely as I'd know if I had a brother or not." No. He didn't say that. And yes, he apparently has a brother – half brother, anyway. Not mentioning it until later is not a violation of canon.
But "relatively unimportant" issues vary by fan.
Most things are relative.
As far as speed goes, when they made the NX-01 faster than Voyager, Berman had only been working on Trek for more than a decade. The Voyager pilot goes out of its way to tell us how super-fast their ship is, "Sustainable cruise velocity of warp factor nine point nine seven five.", then completely forget about it when doing a prequel.
I'm not sure what you mean, but the warp scale is all over the place and quite different from ENT and TOS to TNG and on, as I admitted – mostly due to a poor understanding of the enormity of space, or most people not bothering to make whatever calculations they can.
The warp scale has changed, several times, and its apparent dependency on other factors that are not often mentioned make a difference, like subspace density or subspace corridors or other factors like where they happen to be and where they happen to be going and the subspace conditions that day. Sometimes it's little more than saying just because your ship's maximum speed is X doesn't mean it is traveling at X all the time, or can't even go faster (with the equivalent of a tailwind and drift in subspace, for example). And with Janeway stopping to explore all the time, or the likely off camera lay overs for maintenance and barter with advanced civilizations since handy starbases aren't an option, I'd expect her average rate to be low, despite a warp capability of 9.9 or whatever it was. The 75 year estimate was a best case scenario assuming no short cuts and no delays. It otherwise would probably have taken 200 years. Luckily, with short cuts, it was only 7 and everybody got back before they could legally be declared dead. Ha ha.
As for what Data said in one episode, did he also mention which warp scale he was using? Which episode? Well, it might not matter. What somebody says in an off handed way in one episode doesn't hold up well against what is a foundational fact for an entire series, like Voyager. And like I've admitted, speeds and distances are often not foundational to the story so much so that a simple retcon would fix it (even if it would then appear to be less dramatic)
Who cares? A lot of people do. I find it more mystifying when somebody doesn't, and even almost amazing when somebody seems upset when somebody else does. Fiction of any stripe should strive for consistency, and it should make sense (at least within the given parameters of that fictional universe).
The Vulcan Academy Murders, of course.
I'm unfamiliar, but I know it's not canon, as most Trek stories in books and novels aren't, so if that required a deviation from canon, that's fine since it's not going to become canon and others don't have to live with the consequences. I'm not sure what required a moon, if that's what you're saying, so I can't say exactly how else it might have been done. But if it did violate canon, I'd say it is not as good as virtually the same story that managed to follow canon.