There is probably a minimum size for intelligent brains, but crowd have brains the sizes of peanuts, so I wouldn't think it'd be much bigger than that. Our neocortex is new evolutionary speaking. Often new organs bloat a little, then nature optimizes them. If you already have evolutionary pressure causing them to be small and flying, the pressure should also be there to keep the brain small and change wiring more than size.
I have arachnophobia. Please do not confront me with the idea of an intelligent spider - I'll get the willies so bad I won't sleep for a week!
They're not that smart. According to my half-remembered facts from something I saw on the teevee a few years ago, modern science says that their brains (or functional equivalents) are so small that they shouldn't be able to hold memories. In other words, if something isn't in front of their eyes, they should lose track of its existence. However, there have been tests done where they put a prey insect where the spider could see it, but not get to it without having to circumvent a barrier that would remove the food from its line of sight, and the spiders were apparently able to remember that the prey was there while navigating the obstacle. Hardly Iago. But that does mean that, even if you run around the corner, they still know you're there. Did I mention why they're called "jumping" spiders? But they're pretty cute, as venomous, eight-legged, genius miniature predators that are SITTING JUST ABOVE YOUR LEFT SHOULDER RIGHT NOW go. Pro tip: Don't tell a horror writer, even a wannabe, hell, especially a wannabe, that something freaks you out.
That is one tripped-out tachikmoma! Fun fact*: Jumping spiders recognize** other jumping spiders by eye placement and radius. That same show I nearly cited said that they did experiments with a very small screen TV, projecting altered pictures of jumping spiders and other bugs in front of a captive spider. If the eyes were in the right places, and correctly sized, the subjects reacted as they would to other spiders. Shape of the eyes (adjusted to squares, triangles etc) didn't affect things, nor did the body the eyes were mounted on (like a picture of, say, an ant, cockroach, or Keanu Reeves). As long as the eyes were correctly sized and positioned in relation to each other, the subjects behaved as if they were encountering one of their own. *half-remembered from the TV program I sort of cited earlier. **as in "Hey, that's another jumping spider," not "Hey, that's the guy*** who hangs out over @minstrel 's left shoulder when he's working on his computer." ***
For thousands more years the mighty ships tore across the empty wastes of space and finally dived screaming on to the first planet they came across - which happened to be the Earth - where due to a terrible miscalculation of scale the entire battle fleet was accidentally swallowed by a small dog. (Hitchhiker's Guide)
So my first thought seeing this thread is they're probably going to have an even more interesting debate about the mechanics of flight - especially powered flight - than we did. The fact that they know HOW to fly doesn't mean they understand why it works. They've probably been trying to understand the principles of flight for as long as humans have, for instance, been trying to figure out the workings of our own circulatory system. Flight in their society would have been researched not just as part of the physical sciences but as a subdiscipline of anatomy and medicine. There would have been all sorts of crazy quack debates about why things fly going back to antiquity, and by your industrial revolution you probably have some serious, widespread experimentation in powered flight - likely with a lot of lethal consequences to test fliers. And powered flight would be as important or more important to them than it is to us. They've probably had air war (and air delivery, etc.) since the dawn of time - but powered flight would give fliers unlimited stamina in battle, increased altitude, and enable things like massive troop transports. You could probably also have a lot fun with things like gunpowder and early rocketry - because in this case those sciences are going to be consumed not only with building projectiles but also on in-flight accelerators (a lot of your early gunpowder experiments are likely going to be strapped onto people - with predictable results). The other thing you might consider - especially if you have military components - is that your war commanders will have had to cope with a three-dimensional battle space for their entire history. That means that you probably have some sort of crude three-dimensional map technology to augment 2-D paper maps (I've seen this done in sci-fi with jewels submerged in clear gel, and also markers suspended using wires.) You probably also have a society that's very conscious of air currents, marking them on maps and thinking of them the same way we think about rivers. That's all scientific stuff that might not be needed, and might only exist in the background - but if you have a society of beings that can fly, I'd definitely spend some time thinking seriously about how that's affected their social development, how it makes them think differently than us. Don't just think about surface augmentations, go deep. Also - one thought - can your beings swim? Are they proficient with boats? If not, they may view fish the same way we viewed birds (beings that proved something was possible that we couldn't do). If your race can't swim, water transport takes on a an aspirational role in your society, much the same as we view flight.
Also, I think I've just reminded myself how twisted my own mind is - my first response to "winged, flying society," was "They will blow themselves up trying to fly faster."
The weight-to-strength problem could be avoided by creating a smaller planet with less gravity. Of course, there would be ramifications to that: how to keep an atmosphere from drifting off to space, changes in weather, and so on. But if these could be explained away, I see no reason why we couldn't have flying people. It might be pointed out that on our world, flight among vertebrates evolved not once but three times: birds, bats, and pterosaurs. So it's not too far-fetched to think that under the right conditions, it could evolve in another ecosystem.
Flight gear: Transport harnesses. You can't just put on a backpack when you have wings. And a normal bag would swing and disrupt your flight, so you need special stuff, particularly for heavier things that you can't simply put in your pockets. And if two or more people want to transport something, they need a construction to link them all together. If you fly high, you need protectional clothing or some heating. When you tire, you might like to have a gas-filled sack to keep you floating so that you only have to propel yourself forward and steer. An emergency parachute could also be helpful. And built in a snack compartment!
