That’s pretty much my recipe for suet, too - but I use bear or elk or venison fat or bacon drippings in lieu of the lard. No problems with it melting at all, but I only put it out in the cold winter months; I’ll use Farm $ Fleet brand in the summer months.
We buy Proso Millet in 50# sacks at the Farm Seed store two or three times a year mostly for the Juncos and various Sparrows. Also black shelled sunflower seed and shelled sunflower hearts...