I wouldn't spray that much fabric; my arthritis would flare up from pulling that trigger so many times! Soaking wastes a lot of starch. You do ***not*** want to iron heavily starched fabric while the fabric is still wet. (You can scorch the starch if you iron it while wet, plus you can get the bleed-through problem another poster mentioned.)
Here's what I do:
Mix a 1:1 solution of starch:water in a mixing bowl (start with 2 cups of each for that much fabric). Work on a kitchen island, if you have one. Use a large, inexpensive wall painting brush to "paint" the starch solution onto the fabric until the fabric is saturated. Allow a couple of minutes for starch to penetrate all the fibers. Toss fabric in dryer. Iron with lots of steam (the steam reactivates the starch to get the wrinkles out). This produces a heavily starched fabric that is not quite as stiff as cardstock (seems to depend on the fabric).