Freeplay at the lever: when clutch is disengaged, you should have about 1/8" of play in the lever before it starts pulling the cable.
Also, I always start my bike in neutral. It is normal to be difficult to start in gear.
When clutch plates are worn, you normally have the opposite problem than what you are describing (meaning clutch starts slipping at high speed then slips at all speeds until you just don't move).
As Chili said, problems you described are typically caused by too tight of adjustment on cable or notches in your basket interfering with smooth engament/disengagement of clutch. I've also heard of a too short or worn push rod (a rod in your engine case that actually activates your clutch--it is moved by a cam your clutch cable turns) causing this, but I've never seen it myself.