I've been playing Path a fair amount this league, and I have a ton of points left over from back when I was buying supporter packs, so I can equip us with a full set of specialized guild stash tabs (e.g. currency, essence, etc) if there's any interest. Plus, now that they've decided to push next league back to December, we have more time to play this one!
I'm generally online during the US East coast standard workday (though not necessarily available to do more than trade during those hours; sometimes I actually have to work, or at least attend meetings lol), and then again around 10:30 PM Eastern until about midnight to 1.
I mostly run uber lab (the regular one, not the new level 83 one; that one wrecks my poor excessively-movespeed-focused build). Been doing some endless heist lately too (great way to make some petty cash), and working up a minion character (SRS guardian) to hopefully take care of endgame stuff. Got a pretty good amount of in-game currency, so I can help people out some in that arena as well. Only 12/40 challenges done so far; not planning to push for 40 (did that once; never again) but it'd be nice to get up to 38 for the fancy wings, if anyone wants to try and push for that. Would be really cool to get enough people to do some rotas and stuff.
Anyway, if at least a few of you are interested, we'll need to decide on a name for the guild, and arrange for times to meet up in-game, and ideally someone will be up for creating and decorating our guild hideout as well (I can do it myself, but it'll be pretty drab and boring; my hideouts have never been heavily customized).
So you're right, every so often the challenge league ends and a new one begins, and all the characters and stashes are moved over to the permanent league, Standard. That's apparently going to happen in early December for the current league, so we've got six weeks or so left in the current league. I would generally recommend playing with others, as I find it's easier to play through the game as a group (plus, those of us with more experience have a pretty good idea where to go to complete the quests, which helps a lot). As for how long it takes to meaningfully do stuff, it takes me about 10 hours of game time to get through the storyline to the end-game content (note that this is very slow by most players' standards). From there I'd say it depends a lot on what exactly you want to do and your specific build, but it would definitely be faster and easier with support from others in the form of leveling gear and currency to buy necessary items for build progression, among other things (I can provide labyrinth carry, for instance).
I'm hoping others will jump in here and offer their own perspectives; I think I'm far from the most experienced PoE player on Hexbear.