I don't think Sulman was living in Sweet Water. If he came forward as the / a key witness, I think Roland would have called him such. Calling him an advisor seems a bit much, let alone a trusted advisor. In his letters Roland says, "I am entrusting my advisor Sulman to take care of the detail of informing the families of the fallen as I have entrusted him with so many other things, including the delivery of these letters to you. He will handle the matter with tact, and can be relied on to select the speediest messengers for my letters!"

I can't see Roland entrusting numerous tasks to a complete stranger, even given now naive Roland is. So what if Roland knew Sulman from before, and trusted him because of that? No, I would still disagree. If Sulman had just arrived on the scene after being years apart from Roland, how on earth would he know which of Roland's current messengers were the fastest? If Sulman were a stranger, how could Roland be assured that he would handle matters with tact? No, I think this kind of attitude towards Sulman can only come from working closely with him for many years, where Roland is able to observe first-hand what kind of man he is, and the tone and tenses of his words suggest that Sulman is currently involved at court, not known from the past or from far away.

I read the link you posted, but I can't tell if that is supposed to be official or fanfic; it seems the latter. The story says that the traveller mentions to Xanthor of Roland having been defeated by devils, people questiong the Ironfist reign, and Xanthor glad that problems like that aren't happening in Erathia. Correct me if I'm wrong, but I thought Gryphonheart was already dead and Catherine fighting a war for the kingdom at this point. I don't see how Xanthor could think Erathia free of such troubles if the very survival of the kingdom was currently at stake. In any case, it makes no mention of Sulman. Xenofex has fingers in many pots... Sulman can hardly be his sole agent.

I'm not sure what you mean by archmagi living in huts around Enroth. Perhaps I've missed something? If you're referring to tutors where the PCs can learn mastery of magics, I consider them retired professionals, masters who've settled down and now pass on what they know since they've nothing better to do, when they're not yelling at people to get off their lawn. "Those who can, do. Those who can't, teach." I do not think the prospects for magic masters is as bleak as you seem to suggest. Surely a mage, let alone an archmage, can find work helping Albert Newton with his experiments (he invites the PCs to do so). Or at Gharik's Forge making items. Or at Castle Alamos researching. Or at Castle Kriegspire creating monsters. Or even Castle Darkmoor studying necromancy, assuming s/he doesn't just settle down with their own place as Agar did, and Corlagon, and Ethric (though the latter all happen to be undead).

It's true there may not be a ton of official positions for mages, but that's true for all classes, and I don't think that means that 99.9% of the population is desperate for money. If Sulman is hurting for cash, why not work for one of the merchants? We certainly drop enough coin there for 1000 gold to not seem such a big deal, and it would probably be far safer and pay more than working for alien creatures.

As for Potbello, I'm not sure if he recognized the PCs for what they were. It's possible, and I could see him alerting Xenofex, but X undoubtedly has many other agents around, plus it's hard to have temples raided and priests killed and not get a clue at some point. Besides, if Potbello knew the PCs were fake, why send them on the candelabra mission? Surely you wouldn't send infidels to rescue a holy item? Unless... he didn't actually give a damn about it, and just hoped that the temple would kill off the PCs as it killed off the former priests? Even that is iffy though. Did P know how tough S was, and if the PCs could take out S to get his letter, would they be troubled by rats and snakes? Perhaps S was going to get a lot more gold (the letter doesn't state an amount), but reading that, P made an on-the-spot decision to keep the million for himself and only give out 1000 since the PCs look like gullible fools? "Don't try to say I didn't pay you! You got your gold!" If he did think the PCs were false, AND they killed S, AND they cleaned out the temple, they are cleary some bad-ass mofos, and he should hightail it out of there on the next ship before they're on to him, especially if he kept a ton of gold for himself, yet he doesn't budge.

If you re-read the letters and the other info, you will see that it DOES say that we found the letter on (allegedly) Sulman's corpse. Your idea that the body wasn't Sulman's is interesting. I could come up with several possibilities for that as well. Perhaps having done his work, X had no more need of S and killed him, but forgot his possesions. Some flunky looted his room, found the letter, realized S was killed and the cult is fake and flees into the night. The flunky thinks to cash in on S's reward then disappear, and makes it as far as NS before being killed by goblins. Or, fearful of a trap by X, Sulman sends a flunky to collect. Or, Sulman was killed long since, and his possessions and the letter were taken by A who killed him, only to themselves be killed by B, who was killed by C, until some person who had never even heard of Sulman was killed by goblins. Or, Perhaps S, high on his success and reward was just casting Fly spell after Fly spell to get to NS as soon as possible. When he reaches NS he is out of mana and is then shot down by a dragon tower. No mana, low health, he drops down into the middle of a goblin camp, where they take his few remaining hps. Or, S arrives at NS some other way with low mana and low health. He fights the goblins, and perhaps some tougher monsters, and while putting up a good show, is eventually overwhelmed. Angry at humans slaughtering them all the time, the surviving goblins leave camp and take over Goblinwatch keep. While these all might sound interesting, they don't really fit the facts, and they are a real stretch of logic and plausability.

I'm interested in more ideas or explanations people might have.