I use a meat thermometer to gauge the temp of the scalding water, and use a tall stock pot so there's room to agitate the bird up & down while holding his legs, and get the water down through the feathers to his skin. When the water is really hot I don't have to hold the bird in for very long. And if I find the plucking is going too slowly I can always re-dip him to loosen his pores some more.
I'm going to try that tip of adding a little dish soap to the scalding water next time.
Many of the birds I butcher are extra mixed-breed roos that aren't best suited for roasting. With them I'll slow-simmer them with fresh herbs until their meat melts off the bones, then pick, separate, and freeze for later dishes. But I recently had a couple of Cornish Xs that I roasted (after allowing to rest in the refrigerator) who were dee-double-ee-LISH-ous!!!
I wish you great success as you learn to process & prepare your home-grown meat birds, and many many delectable meals!