Just how old are Matt and Alex, anyway?
I'll admit, this is tricky to figure out, given my drawing style throws proportions off madly and makes everyone look like kids. Sorry.
But, as a rough guide, as per the start of the comic, Matt is around 23-24 and Alex is around 22-23. For the curious, Phinn is in her late 60s (but she's an elf, so she's actually fairly young), Jacob's around 21-22, Salthalus's true form is in her 70s, and most other characters can be derived roughly based on this data and how they interact with everyone else.
Note that all this is somewhat variable and subject to change slightly.
What are those odd things that look like noses with feet, eyes, and wings?
Those would be Nasal Flies. They are the result of a completely botched spell. While it IS possible for the mage to accidentally get an effect that he or she wasn't looking for when casting spells, it's also possible to get nothing but one of these creatures appearing with a characteristic "THUNK" noise.
Nasal Flies don't have much in the range of intelligence. They just sorta fly around randomly until their lifespan ends, then they just poof out of existence. Larger Nasal Flies live longer and come from more powerful botched spells.
Basic story, it means someone's either trying to cast a spell they don't know much about or something stopped them from finishing a spell.
How big is the village Matt and Alex live in?
When I first came up with the comic, it was a tiny village of only a few regular people, set on the edge of a small wooded area. Except I realized that Phinn's library wouldn't really fit well in a tiny village, so that idea went out the window quick.
Regardless, it's still a relatively small town. I don't have exact measurements or population data. Nor a map. Sorry about that.
Where is everything in relation to everything else? How big is the Landis Kingdom and the surrounding lands?
Laura Taylor made a map of the DoM world thus far, insofar as she could determine from in-comic dialogue. And to be honest, that's pretty accurate to what I had in my mind when I was thinking about it. So that's as official as it'll get for now.
As for distances, however, that's a different story. In the same vein that I never really nailed down an exact size of Alex and Matt's village, I never really got the distances down pat, either. Some of them have been described a bit, such as it being about a week's worth of walking between the village and Lineta Hall, but other than that, distances are (somewhat intentionally) vague.
When we first saw Marzos and Stephanie, they seemed to be able to teleport themselves around all over their respective places. Why don't we see this happen later with Marzos, and why don't other mages do this?
This is one I thought I'd have a chance to explain better in-comic, but as it turns out, I was sort of wrong. Oops.
In both of their cases, the assumption is that each set up the places in which they respectively lived at the time (Marzos's cave and Stephanie's grove and house). That is to say, they could teleport around where they lived because they prepared it ahead of time. That's why Marzos couldn't immediately give chase to Matt, Alex, and Vince when they fled the cave, nor to Cy, Eddie, and Winslow after they destroyed the poison supply, and why he wasn't shown just poofing all over Sunlit Tower at Lineta Hall. That's also why Stephanie was forced to run from Matt when he chased her from Castle Landis back to her grove, and why she was able to simply vanish once she got to the grove itself.
Of course, in Stephanie's case, she isn't that slick of a mage to begin with. Given enough time and drive, she can come up with something (such as Simon's condition and the modified ice rose poison), but for the most part, she just lacks the patience to get good at it. That's what the odd pinkish ball Simon found was supposed to be about; the implication was going to be that the teleporting through her house and grove were set up by or stolen from someone else and she required the magic in the capsules (which, presumably, she could replenish) to pop around as need be, hence why she didn't poof out of the main lab (she dropped the one Simon later found, but was still able to improvise a solution to save face until Matt caught on) and why she was forced to stop and fight Matt at the end.
It's just that the chapter was getting long enough as it was (not to mention the horribly-paced fight scene at the end) and I couldn't find a good way to explain all that in-story, so, well, sorry about that.