When I started the KU, I advertised all over the place heavily and got about 10 folks. Over the life of the game, 4 years or so, we had about 24 players through. I was surprised too, as I thought if I build it they will come. Be prepared to run numerous smaller factions as the GM and be ready too step in to play big factions as players come and go.
As to playing, I still have outstanding work for Kwic and Dragon Cat, on top of the stuff that I need to do as a BattleTech Volunteer, so playing is out for me.