New service panel energized, "Cut and Swing" complete.
New backed up loads panel, 125A bus, 100A main breaker now fed by load-side tap from 200A service disconnect (same for PV disconnect switch and future 200A panel to replace old panel and meter.)
For now this panel has 40A breaker for oven, and 40A breaker backfeeding old 100A panel (which has no heavy loads actually used.)
The interlocked breaker top right had been receiving backfeed from old panel. Next it will go to a 30A 120/240V inlet plug for generator, later to be 100A from inverters.
I will transfer remaining circuits over from old 100A panel to new panel, rip out old panel/meter socket/riser, then install new 200A panel. It gets 3/0 feeder tap from Polaris in main breaker box on front of house through 2" conduit, 3" conduit to a box from which Romex can fan out to other loads and 2" to box under joists connecting everything I've installed.
I can run one more 200A circuit. Don't expect to unless I excavate a basement workshop, but have taps to make the connection.