Although this is an old question might add my two cents worth after going through this at my organisation.
We have two accounts, enterprise and standard for distribution through the iOS store, each account has max 100 (not sure if this was different earlier but thats our current limit). Most developers are added to the enterprise account.
Unless you have a massive amount of developers and I doubt any would if they think about it only developers should have their devices on the account. Once it needs to go to clients or shared not for public use we use ad-hoc distribution which doesn't count towards your device id's.
We also petitioned Apple for more devices and we got an additional 10 which didn't really solve the problem.
With regards to the private key, you should never distribute it. It's a major security vulnerability.
