MarkDH

Eek, don't worry for now as I have just discovered that the COM library has been extended to manipulate HIDs since I printed my FSUIPC documentation! At first glance I am hopeful I will be able to do what I need with those functions with the VID and PID.

Personally I would say don't bother with the Saitek switch panel. It's okay (although one of the two I bought stopped working) but there are two reasons I say this. First, it is very specific to a particular class of aircraft and you will find yourself (1) trying to find out how to reprogram it (SPAD, FSUIPC, LINDA) or, more likely, (2) just not using it. The other reason is really (2) again - you may find yourself just not using it anyway except for a few light switches. I built a whole Twin Otter cockpit and there are some panels I just don't use. So spend the money on what you will use every flight - TPM yes; yoke or joystick or pedals, yes; autopilot or GPS, yes; radios, yes - and so on.
 
While I'm on the subject, I have spent a lot of money on Saitek stuff and a lot of it's junk. It looks good and some of it even works okay (rudder pedals, Cessna trim wheel), but some of it doesn't (radio panel, "pro flight" yoke. I would recommend the VR Insight multi-panel as a general programmable panel - it is excellent quality and has a good collection of rotary controls, analogue sliders, toggle switches and buttons. It is, however, expensive!
 
As for yokes and pedals, it depends what you're asking. If you already have a joystick and it works well then adding a yoke will not make a world of difference. Most likely you will go backwards because you will buy a cheap yoke like the Saitek (junk) and it will be worse than your (likely cheaper) joystick for controlling the aircraft. I have reviewed the Saitek, CH Eclipse and Elite yokes in some depth on my YT channel - follow the link in my banner to find those reviews. Pedals, I think they add a lot mostly if you want to operate realistically in crosswinds. For the flying part you don't really need them unless you're flying gliders, although it is cool to be able to side-slip an aircraft aggressively (subject to flight model) to finesse an approach.
 
Hope some of that helps.