1. I wouldn't challenge a pilot for being 5 kts out, especially in a descent as the wind changes. Most modern airliners can fly a heading exactly to the degree, and should be able to
2. Speed reductions in the descent aren't the easiest thing to do especially if you've given the aircraft a level by point - in that respect I'd usually want the aircraft to make the level first and then reduce the speed. If it's the other way round, you would definitely expect to be told. For climb/descent instructions, I think there's something about 30 seconds somewhere. In the UK en-route, we get alerts if a climb hasn't started within 20 seconds.
3. Yes unless stated, although you often don't get told by A340 pilots struggling up the last couple of thousand feet using curvature of the Earth (other makes of plane are also guilty)
4. If you want someone level at a point and route them to somewhere else then the level restriction is no longer valid unless restated in the clearance. IE: be level at Point A, if you then route the aircraft direct to Point B the clearance to be level at A no longer applies unless specifically mentioned