The Level 3 HP Monitoring bundle mentions it includes an emonHP.
Which hardware and software guides should I be reading here, please?
The emonPi one? emonPi User Guide — OpenEnergyMonitor 0.0.1 documentation
I have registered for an account on emoncms.org and heatpumpmonitor.org
Anything else I should do in advance of the install please?
The main guide can be found on the shop page here - emonhp.pdf (openenergymonitor.org) When mine was shipped it came with a hard copy with passwords and credentials for services.
Once you have the hardware it it pretty much plug and play provided you know how to plumb it in and wire the electrics (you may want trained professionals / your heat pump installer to do this for you).