In diesel school we saw many different procedures for break in of new engines. after starting and checking for leaks, coolant level and oil level, John Deer recommends running the engine at rated load and RPM for 15 minutes on some of the engines we rebuilt. Most of my friends when they drive new truck or break in new engines, hook up to a gooseneck with max loads for a few hundred miles. This really helps to seat the rings and get the carbon built up around the top ring land. changing the oil at 1k is a good thing, it will look like a gallon of glitter was added to you oil from the rings seating.
As far as additives, do not run anything that makes the oil super thick or radically changes the viscosity. This will keep the rings from seating into the cylinder wall properly and will lend itself to more blow by. Zinc and phosphorous alone more or less just get the oil back to factory specs from a few years ago plus a little. Steer clear of a lot of friction reducing additives during break in.
Zach