Re: PCs hiring adventurers
Well it's really up to your DM. Personally, weather I rewarded EXP or not would depend on the actual RP around it and the method.
On a pure system level, you didn't really preform the deed yourself. But at the same time, exp is earned from good RP too. You did solve a problem. Personally i'd have awarded exp for a "minor" quest completed. Now, weather the message would actually arrive is a diffrent story. It kind of depends where you're sending them, right?
You gotta consider that any adventurers beyond the PC's are NOT, in fact, PC's or even main characters. Their stats and abilities, both system and fluff wise, are inferior. Chances are they may not pull it off if they get jumped or the like. So you have to be ready for the worst case scenario of the message and/or package getting lost. Especially if this is a hard-ass DM.
It's definately an option, I'd definately allow it. But you'd have to consider adventurers are not by default honorable. How do you intend to pay them? If they need to return to you or FIND you to get their reward, they may not be eager to do so, as getting the compensation may be harder than the actual task. And if you pay them in advance, chances are they'll just run off with both payment and delivery. And if you just sit around waiting for them to finish the mission, the entire point of hiring someone else to do it becomes mute, as you have to wait for their return either way.
All of this can be solved, of course. And it is very fluffable. Perhaps theese hirelings become a sort of contact for later use. Or maybe it evolves into some sort of side story with new side characters. Hell, if there are enough players, perhaps a secondary party can be started (with other players than yours, mind you) playing this group, this being one of their first adventures. Parties being played in tandem like that can be difficult but the result, with a capable DM, is sheer awesomesauce.
solving the problems listed above also works with fluff. Your character gets to be clever, display his ingenuety and mastery of magic as a wizard in bypassing the issues of this undertaking. Heck, perhaps you even skip the whole thing and just send your familliar. There's nothing to build up a powerfull wizard than being too busy to appear himself, and instead magic-ing a minion or hireling in their stead.
(excuse any typoes. Posting from work. Oh i'm a bad boy.)
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