You have a transfer pump on your tank ...right ? 12v ?
if you raised the tank do you think the Zeta would gravity feed OK ...
what is the min temp setting ... could the pump handle the heat from recirculating the water at 250psi without damage
Is there a minimum 'total' jet size before low flow would cut out the burner ... 
As long as you prime the pump on the zeta it will draw from a tank no problem, in the past i have used a sureflo demand pump but it really in not necessary as long as your tank provides some flow.
Min temp is 30 deg C and Max is 90 deg C
If you want the Zeta to work without any pump problems then dont feed hot water into the pump inlet, i am currently working on adjusting the flow switch to switch the burner on at lower pressures.
At the moment the machine works well with a twin jet wand with two 0.3 jets, smaller jets give higher back pressure which means you would have to increase pressure on the machine to fire the burner.