If I do a mash like that, I just bring water up to 120 f and hold it while adding rye. I use a beta glucanase. Add it, get you rye in hold it about fifteen mins, the slowly bring temp up to 145. Hold about fifteen mins, drop to fermentation temp and ferment. I shoot for 12 brix on a beer still, 15 on a pot. The warmer you ferment, the spicier the profile.