Rotameter works great for this.
View attachment 410060
I've found that my max achievable flow rate without sticking depends on how deep the bed is.
Few other things:
-Malt conditioning has been mentioned. This will help keep your husks more in tact. Even 1oz of water from a spray bottle makes an enormous difference. Also keeps the dust down. 1-2% as mentioned i think is more than needed and just gums up the mill rollers.
-Milling slower is better. A variable speed drill with an adjustable trigger knob lock is great.
-If you have a sight glass in the tun it will indicate the pressure across the bed. Use this as a guide for when you're going too far.
-Dough in low, i target 131 and give it time to hydrate the starch. This prevents dough balls from forming.
-I picked this one up from low oxygen brewing, but it would also work great for normal brewing - underlet the mash. In essence you fill the tun from the bottom up, which displaces air and fills the gaps between the grain slowly. This combined with the dough in at 131 makes a big difference. You still need to give it 1 really good stir in the beginning though.