Having done several partial mash beers,I'd say the hardest thing to get a handle on is a steady mash temp every time. The size of the mash (water & grain volume) is important to this as relates to the mash tun size to hold the heat in & steady for the 1 hour mash. I learned this with my first stout this time. 4.5lb mash with the right amount of water needs a smaller mash tun that 5-6 pounds of grains with 2 gallons of water. The right size kettle or whatever you mash in has a big impact on how much temp loss there is,or how much temp it holds or gains. If I mash 5-6 pounds of grains in 2 gallons of water in my 5 gallon BK/MT,it generally gains a degree of temp in 1 hour.
But 4.5 pounds in 1.5 gallons of water went from 155F down to 142F in that hour. Less volume,less heat that gets held. Lesson learned there.