1. Yes, in HKG you can store your luggage at a place located on the arrivals level between the two exits from baggage claim. It's kind of expensive, as I recall.

2. Don't know.

3. Yes, there is a manned transfer desk available before you hit immigration.

4. The departure tax is 100,000 rupiah and I suspect you will be exempt as long as you remain in transit (I've never done this, so I'm just guessing based on the fact that the payment of this tax is verified before entering the departure hall, rather than at the gate).

5. The lounge is okay, but nothing special. It doesn't stand out in my mind as being particularly good or bad. It's definitely not worth special mention.