I like it at 1.6 qt up to 2 qt if it'll fit in the tun depending on recipe etc...
For your first run you could keep it on the thinner side and throttle back the flow a bit after the grain bed sets. YMMV If you start with a trickle and then open it a bit more you'll see about the time it sets is when the line fills all the way on it's own but you'll also still see some chaff for about a quart or two. Run it too hard and you'll compact the bed with gallons of wort on top.
If that happens just stop, stir up the mash and start all over again. No biggie.