If it was me. I would be buying;
The shurflo 5L a min pump.
John guest push fit fittings. (so 1/2 inch bsp screw thread to 1/2inch push fit john guest)
Analoge controller as mentioned.
Pump Strainer (again with push fit fittings)
Bone dry system can be easy achieved with push fit fittings.
I'm with Pure on this one.
I have had nothing but Varistreams and they have served us well. But as Pure says, the flow control side isn't good enough, 3 is too slow so you have to live with 4 even although it's a bit fast. The other issue is battery usage which again Pure has highlighted - although easily remedied.
My son still has the analogue Varistream in his van and the dial for setting the flow rate is awesome. Having to open the front to adjust the pressure setting was its Achilles heel.
The only thing the analogue controller hasn't got is a built in volt meter, but they are cheap enough on Ebay if this is a real need.
The analogue controller is certainly the next controller on my shopping list when needed.
I would also buy a Shurflo 5 litre pump. They have never let us down since adding Varistreams to them.