1. Yes, but keep in mind that your headphone cueing situation will depend on your device as you can't use multiple audio devices within rekordbox.
2. No, but if your device doesn't have ASIO (only has WME or another driver), you may want to reconsider as low-latency ASIO is important.
3. No, see #1; you can only use one audio device within rekordbox.
4. No, see #1.
5. Probably... but no harm in playing around!
6. Not likely due to cost.