I've been watching this thread for a while, and it looks intriguing. Here are some thoughts I've been pondering.
1. Goal and purpose of the organisation: This is quite important. So far, I've only seen a general idea/ideas about this organisation - so could you try stating it explicitly? Is it the one in the first post of this thread - the Vagabond part?
2. Skills required: If you're going to be venturing out of Syliras far enough that the Knights can't protect you adequately, there needs to be a minimum level of wilderness survival and basic combat skills. I understand that there is a group of Syliran Knights based in the Bronze Woods, but there'll still be plenty of chances to do good.

You could still try to wing it in a group, but spending long periods out there is inadvisable. Of course, if you're a ghost, then it won't really matter unless you meet a hostile Master Spiritist

3. Active PCs: This will determine if your organization will last or not. There's been a few PC organisations in the past, but most of them have pretty much petered out due to lack of interest and/or inactive PCs. A few people need to be running this organisation and also be actively posting and creating opportunities for members - the last part STs could do though. Now, this might be a little too early to be thinking of such things, but if you're keen on making this whole thing work, do try to be on Mizahar as long as possible - and posting on a regular basis helps too.
4. Relationship with the Syliran Knights: Well, you'd have to deal with them sooner or later. They might see you as muscling on their territory, they might see you as a big help... If this organisation is going to be active, I think you might want to appoint someone to act as the liaison, the go-between to settle anything between them.
5. Income! Ahhh, mizas, mizas, mizas.... But in all seriousness, how is this organisation going to settle this? If you were, say, a volunteer organisation where people can sign up for duties and do good things for free, then it wouldn't be so much of a problem. But making this into a legit, for-profit organisation could require a proper headquarters, financial and other resources, and maybe even hiring trainers to train members (or members could train other members). And would you want to make this be a job for the members i.e. they get paid every season and all? Earning money would be hard, and you might have to make this a business to settle this problem. Then again, the Syliran Knights could fund you. Another option would be to support the organisation with part of your own personal incomes. The organisation would collect a seasonal fee from all of its members and try to use it. This, I think, is a viable idea.
6. Masks: Now, don't get me wrong, masks are awesome. I've been to Venice once for the Carnival and it was awesome. Intimidating masks, masks that inspire fear, wouldn't really endear the members on duty to most people - OOC-ly, this isn't much of a problem, but IC-ly, you might be trusted at first, and there could be a problem with trying to raise your reputation.
To be honest, I'm glad you're not doing something terribly overdone - like an assassin's guild. Not that that would even work in Syliras. This idea of yours has great potential, and if we can hash something out of all this discussion, I'd be glad to help develop this further IC and OOC. Crypt is going to Syliras as soon as he's done with the Kalea Regional Quest (I don't know when that'll be) and he could possibly join in with the fun. I hope this can go somewhere, so good luck! Cheers!