Maybe Calum or Lightspeed will advise about the extension hose? A grease gun hose was mentioned earlier as being suitable and that sounds good to me.
You probably can set the SPA gauge up on a bench prior to installation but it will still be equally fiddly to do as installed. It has a multifunctional button that requires lots of presses in different menues in the set up. At least you only have to do it the once really. One thing I would say is to use the pressure "damper" option so that the display changes slowly, say a 2 or 3 second setting or the display is just a blur of constantly changing numbers.
If you don't have heated seats then there is a spare supply for that you can use for power, or just splice into an ignition load 12v supply. Make sure you don't get the grey/black lead near the fuse box as that will be 5v and is for the speedometer calibration mode switching.
