If your players want to run in the Kalamazoo-Grand Rapids sprawl, more power to you. Keep your numbers realistic and you should be fine; keep your
reasons as realistic as your numbers. Who's active in the area? It may not be Ares and Saeder-Krupp and Shiawase, but it might be 'small' corporations (Kellogg's is just around the corner in Battle Creek, after all) that are 'beholden' to a larger one -- or perhaps they're all Ares allied (HQ in Detroit) and it's more a question of 'get paid by everyone else to run against an Ares subsidiary'.
Note that numbers results in ... hm. What did we figure, back in the day ... basically it amounted to, per million:
- 20 deckers/technomancers
- 20 mages
- 25 riggers
- 25 faces
- 50 street sams / martial adepts
This resulted, generally, in 25 teams, with a mage/decker/technomancer sometimes working with two different crews. There were also 20-25 fixers, who often worked with 2-5 different teams each, so there can be some competition there, but the fixer game is a matter of who you know, not whether or not a team works only exclusively for you -- because not every job is perfect for every crew, and sometimes you need to mix and match.
Shadow-active people, therefore -- that's shadow
active, those connected and working and working closely with the guys who do the bad deeds, fixers and shadow mechanics and talismongers and street docs and the like, but NOT your bartender who keeps his ears open, or the bum you can count on to keep an eye on your stuff for a bottle of synthscotch -- are at most 0.1% of the populous -- one person out of every thousand. That doesn't sound like much, but in a million people, that's a thousand shadowfolk, only 150 or so of which are active runners. Everyone else is, in some way, support personnel. (But not Johnsons. They fall into a different category.)
All this is an aside, really. So long as everything hangs true and CAN be hung on SR in general (which really is an easy thing to do -- a Kalamazoo-Grand Rapids sprawl might have evolved after Bug City in '54), you're pretty good to go.
As for obsessiveness, well -- we did Cincinnati the same way, and others have done lots like that. You're not alone. Now if only we could collect them all into one place ...