Other people please feel free to chip in.
They do regulaters that feed two things, they might be called a twin or something, i expect that is what you need.
As for lenghts of pipe i have used several.To start with i used hoselock and garden hose.On exit from the heater this used to balloon up and explode.I then used car heater hose.This was okay but hard to work with.
When i started a two man set up i had problems with 'sucking in' of pipes.(i was sucking rather than blowing)
What i have now may not be applicable to you but the list is.
To heater cold feed from tank garden hose hoselock
Heater exit; shiny metal flexible threaded connection to 6" white pipe that takes little inserts, to
Tee piece of white pushin pipe, short lenghts coming out to elbows, to short lenght of white pipe.
This is then pushed into some really thick blue pipe that has a white inner- this is flexible and you can do anything wiht this- this blue pipe peter may sell i don't know-.The white push in bits you get from a builders or plumbers merchants.
To finish blue pipe more white pipe shoved in, then to a push in connection that screws to pump.
If you are one man, then flexi metal bit, with white pushin shoved into blue pipe, short lenght of white shoved in at other end, then push fit into screw on connection to pump.
Others will have different ways of doing it.The simpler the better, but remember you may need to disassemble if it gets cold.
If you are two man and plan on putting the heater before the pump it must go as low as possible.If the heater is after the pump this doesen't matter so much.