A whole lot of work for a few extra litres fuel.
Running duel pumps hmm a simpler way would be stick the existing pump filter and reg in the aux fuel tank and feed the aux tank from the main tank by gravity through the existing fuel hose 1st leg.
Then 2nd leg of existing fuel hose would be the pressurised supply from the aux tank to the injector rail.
Of course the pump filter and reg will occupy volume in the tank so will cost u fuel space in the aux. But u would gain space in the main tank.
Still. Seems a lot of work and expense for little gain. Custom fabricated anything is expensive
You could upgrade your motor and then will need the airbox for a 2nd battery, adjustable fuel reg or traction fluid catch can
To answer your other question our fuel system runs at 3 bar