1. I believe the minimum legal interline is 60 mins, so if the CZ runs at or close to schedule than you will be fine. HKG is a very efficient airport - CX to CX MCT, for example, is only 45 mins.

2. Not sure, but I'd be very surprised if not since CZ looks generally like a full carrier. Maybe others can confirm.

3. That is a UA specific question, but if this is the first segment of the award then it is definitely a risk in principle, but I'm pretty sure you'd be able to sort it out at the UA transfer desk or lounge at HKG.

On the other hand, a 3:35 layover at HKG isn't too bad a thing - there is lots of shopping, eating, internet cafes, etc. even if you don't have lounge access.