Using software, lately Brewers Friend, calculate strike and mash temps....
Add grain to bag(s) 2 or 3 usually to reduce weight as stated above.
Unless dong a German multi step mash, simply add grain already in bags to strike water at strike temperature, say 163 F or so. Cut heat.
Watch temps drop as I stir grain in bags to break up dough balls.
When at mash temp remove BK from heat and place in sleeping bags/ blankets etc for one hour.
My mash temps hold very well.
Hope this helps.