The maximum contacts you can have is 300, so THAT's no problem.
I've heard suggestion that you add only 5 at a time, then wait a few minutes (and/or exit/reopen YM) to let those be assimilated before adding more.
But as for the "Pendings", no idea. I've never had more than 3 on Pending at any one time.
A minor(?) related problem I have - at times I add someone, and they stay as Pending. When I ask them later they say they never got a request to authorise me - and there then seems no way to "re-request" short of deleting them then re-adding (which usually works fine the second time).
Interesting question, TC61 - I hope you do come up with a clear answer.
