Have the HRE stay united early on in it's life. You would hava e great state in central europe, encompassing the low countries, germany, the alps, bohemia, eastern france, either northern italy or all of italy. Plus the teutonic crusader order in prussia later on. Germany north of the alps would become majority german and the grand heartland.
With the ports in flanders and to the north sea you could see them having similar colonies to the dutch like the east indies, sri lanka, south africa, brazil and maybe oceania.
The germans were given rights to colonize venezuela, we could see this become a reality. Maybe forming a union with the colony in brazil, and if they colonize argentina.
Large amounts of immigrants would arrive, especially after each great war. Minorities of the empire like italians, poles, french and bohemian would emigrate en masse to the colonies.
I would recommend watching Whatifalthist's video on it.