Syndicate Members and Level

One of my players wants to create a Syndicate made up primarily of spies (4th level thieves). Is there any reason why he shouldn't be able to? I can't really think of any, except for a nagging suspicion that there should naturally be more lower level members because that's just the way things work. Like, otherwise it would be a kitchen filled with chefs and no dishwashers and busboys, or a military filled with officers and no grunts.

Along this line, are there good guidelines for:

1. Determining the value of hijinks a Market Class can support (like, there are only so many rumors one can learn).

2. Determining what happens when a Syndicate is established in a community that already supports other Syndicates. I've intimated that this will likely result in the established Syndicates strongly suggesting that the new Syndicate needs to pay them some dues, followed by potential gang warfare. I've assumed that the other Syndicates will become aware of this new Syndicate after a certain time (based on the income the new Syndicate earns from their hijinks).

i think several people on the forums have proven that building a syndicate predominantly out of spies ends up creating bonkers amounts of money, and the rules as written offer no reason you can't do this.

Since you need to recruit them I propose secret loyalty rolls and if the player doesn't implement various costly protective measures such as a cell structure, spies who deal in internal affairs etc. a disloyal spy will sell out the spy ring and either bring down the wrath of some other organization or simply make them much less useful if everybody knows their names and faces. Basically, the problems real spy rings face. I suspect there is a reason why organized crime is often run as literal families with blood ties while national spy organizations are very vulnerable to double agents. Perhaps some sort of rite involving monthly or yearly ESP - sessions to find out potential turncoats, like the D&D version of a pylograph test.