Firstly welcome to the forums, I hope you will find us friendly and helpful.  And congratulations for being interested in renewables.  

Heat pump control systems are certainly more complex than EVs or Solar panels, fundamentally due to the complexity of the (seemingly simple) problem of heating a house to a comfortable temperature and doing so whatever the outside does and indeed whatever the design of house is.

Posted by: @renewables345

↑

controls, sensors, and integration with cylinders or multiple zones.

The simple rule (with the caveat that every rule has some exceptions) is DONT use any external controls which are not specifically designed for heat pumps, of which there are currently only 3 to the best of my knowledge namely Homely, Adia, Havenwise.  Almost all other external controls will conflict, in a bad way, with the heat pumps own controller.  You wont necessarily know it but you (or rather the customer) will pay for it in running costs.

Heat pumps should generally have the minimum controls possible other than those provided by the manufacturer, basically operated on weather compensation with possible a little room influence but generally not much. Mostly single zone too, not multiple zones unless the house is very unusual.

If any 'Smart' control manufacturer (other than the three above) tells you that their controls are suitable for heat pumps (a) doubt the statement and (b) ask how it integrates with the heat pump bus/weather compensation curve.  If you get a blank stare or BS, walk away.  Plenty will try to give a swish sales pitch, but generally its not worth the paper its written on.

Thats the starting point, if you want to understand controls for heat pumps, as opposed to simply following diagrams drawn by others (often generic designed to apply to all possible cases and thus include lots of extraneous stuff), you need to get your mind round this and also why its the sensible thing to do.

Sensors, other than those in the ODU itself, are generally limited to a thermistor for the DHW temperature and maybe an OAT sensor to be placed on a wall out of direct sun.

Beyond that you need to learn about the controls in the plumbing as well as electronic controls, because these are part of the overall control strategy and cannot possibly be separated from the electronic controls when thinking about the system.  The only necessary one is a diverter valve (DHW or space heating) but there are often TRVs or UFH mixers.  Both of the latter can be bad news and should be avoided, or set above the desired temperature, to act as limiters not controllers.  Ideally you shouldn't need a UFH mixer. 

Static adjustments by LSVs or the UFH equivalent are an important part of the overall picture.  These are set once and forget (albeit via an iterative process in most cases), but vital to getting the system operating comfortably.  In addition to the above there are some safety mechanisms associated with the pressurised parts of the system, not really controls.

Posted by: @renewables345

↑

Could anyone point me in the right direction for learning resources? I’m particularly interested in:

• Wiring Layouts

• Good training courses (online or in-person, ideally UK-based)

• Videos or books that break down common setups and troubleshooting

If you’ve learned from experience, what helped you most when starting out? And are there any common pitfalls or mistakes to avoid?

Most if not all heat pumps have a wiring centre either in the ODU or separate, to which all sensors/controls should connect (and if they dont they probably shouldnt be used, but sadly often are).  These are manufacturer specific but of course there are common themes.  Download a few installation manuals and you will see what I mean.

In addition all heat pumps have an installation menu in which a whole host of control parameters can be set up.  This is a vital part of the commissioning process.  Unfortunately its not always obvious what any particular setting does and, while the concepts are similar, the implementation differs from manufacturer to manufacturer.

For more general instruction you could do worse than look at some of the heat geek videos.  They cover much more than controls but in order to understand the controls fo9r a system you need to understand the system!  Other than that I cant suggest anything particular, others may be able to

I would sound a strong warning that there is a lot of poor material around evidenced by the number of poor installations seen.  Thus view anything with a pinch of salt and try to get to the bottom of whats really happening, whats really necessary (and what is just an unnecessary and frequently destructive sales gimmick), and why its sensible for a heat pump.  Heating control manufacturers have brainwashed us into thinking that micro-zoning in time and space is a good idea.  It certainly isnt for heat pumps (and very likely not for many boiler installations)  There are good reasons why this is the case, look at some of the Heat Geek videos on zoning.

Finally heat pumps need generally either a 16A, a 32A single phase, or a three phase feed for the higher capacity ones.  Best practice is RCD protection (I think generally Type B), and some heat pump manuals specify or encourage this; the IET regs require only MCB protection for external fixed plant unless the electrician assess that the risk is sufficiently high to merit RCD.  This is a point of occasional consternation.