You can do all this with the H8000, although I'm not so sure about the reversing. There is a Reverse Sampler preset, but I'm not familiar with it.
There is always a certain latency with MIDI. It certainly takes a millisecond to send a MIDI message, and then it takes a certain time to respond to it. I'm going to guess that most units (not just ours) would take maybe 30mS to respond. This is about a film frame.
If you really need minimal latency, you'll have to look for it – this is not something that is usually specified. My guess is that a hardware unit would be better than software in this respect.
