With that many Linkedin connections, how are you able to manage or be engaged with them?

Not all 100% of them, but I do take the time to get to know the people in my network (if I already do not know them or interacted with them).

Be it 5, 10, or 15 people a week: by ECN, phone, Skype, or meeting in person -- that's how I engage with them.

Sometime, I too have to be selective who I give my valuable time to, and that takes effort to.  But I manage well.