1) Horde is better (in terms of population and progression, at least based on this past expansion, dates back a lot further than that though). The community has been dwindling for a long time, and we <Ropetown> have been #1 for as long as we have been on the realm (we are no longer raiding 25 man come MoP, and haven't yet figured out what raiding plans there are if any, so all of that could change). I'd post more about how Horde is better than Alliance, but it'd be a bunch of BS. Both factions suck pretty bad at the present moment, and there's not much to be said if you exclude raid progression. There's like one team in glad range on either faction, and RBGs don't exist here anymore. It's easy to find pugs and stuff on either faction (allegedly), but the quality of those is hit or miss.
2) The economy is pretty awful (at least in comparison to high pop realms such as Tichondrius and Kel'thuzad, the only 2 high pop realms i bothered to check out), but that has more to do with where we are in the expansion. Through out Cataclysm and WotLK the economy was pretty stable and had usual patterns you'd find anywhere. Some items were more expensive for longer stretches than others, but in all, it was OK.
3) As far as a levelling guild goes, there really aren't too many. Most guilds raid (at least in some capacity) but there are some guilds that have people levelling in them a lot, and you probably wouldn't have trouble finding somewhere friendly to level up, especially if you have experience in the game, and can make friends easily.
Hope this was helpful, I've been on Executus most of the time I've played, and have played both factions here.
There's room for friendly, knowledgeable people anywhere, hopefully you're one of those!