1. What is the general backstory of the Mummers? How did they form their loose organization?
They don't have a particularly detailed history as an organization, as it's a loose group and more of a natural gathering of like-minded individuals than a structured organization. It's fairly typical that groups of actors and performers will get together to form troupes and such. It's more likely that particularly passionate performers and similar people find they have the gift, to varying degrees, to channel their emotions and thoughts into their performances. The Mummers, as a guild (such as it is - they're not particularly structured), aren't the only ones who have such abilities, but they're the most concentrated group. Statistically (and lore-wise) speaking, very few Mummers possess the abilities to the degree that player characters do. Most Mummers are simply mundane actors, performers, musicians, loreseekers, poets, fortunetellers, performing charlatans, and so on.
There are some famous historical figures who could be considered Mummer-like, in that they were either extraordinarily charismatic, or that their ability to mesmerize and ensnare/manipulate was notable to the point of being considered supernatural. One brief example is the legend of Sifa the Golden: a woman who rebelled against King Gudleifr, most infamous tyrant in the history of Aetgard (now the Lost Lands). Not a skilled fighter by any means, Sifa used her extraordinary charisma, charm, and influence to get the people to stand up to the tyrant king. When the resistances and rebellions ultimately failed, Sifa led many of the people away, south through the Fey Forest to the hills of Karnath. These people ended up being known as the Hillfolk. Sifa later returned to Aetgard, gave herself up to King Gudleifr, and requested that she be able to perform once more as her last free act. She then ensnared the king and his court with a combination of song, dance, and playing her fiddle. As Gudleifr's officers stood mesmerized, Sifa led the tyrant king out of his keep, out of the city, and into the forest - neither to be seen or heard from again.
2. What can we expect to see Mummers doing in the somewhat near future as far as abilities go?
Expect mostly roleplay abilities with minor mechanical applications (if any). They aren't intended to be a powerful guild. Though some of their Words, and Mind Fog, make them extraordinarily capable crowd controllers and "debuffers", this doesn't mean they should be expected to have a prominent place in combat, and their abilities will not be tailored such. They'll likely have some abilities that give minor benefits to those nearby via inspiration and resolve.
3. Will there be dedicated skills for Mummers in the future?
Not sure what you mean by "dedicated skills". If you mean skill trainers, then yes.
4. Do the extraneous items and wagons in the Camp serve any purpose aside from cosmetic? Be vague with this one, I don't want a straight answer, and I'm willing to RP for answers on this subject rather than get them through the forums.
Maybe.
5. Can we get a basic idea of how channeling effects guild powers, if it's meant to do so at all? My character gains very small amounts of channeling skill per successful Word usage now.
Channeling skill slightly influences Mummer abilities, as they're based on channeling emotions and feelings outward from the Mummer himself. Other factors I prefer not to reveal. The Channeling skillgains (and guild points!) were only just recently added.