So the main panel for the entire house is only 100 amp, and you'll pull 50+ to the garage.
I suppose that would work if you have gas heat, dryer, range. Or maybe the 100 amp panel you've shown is a interior subpanel and you have a 200 amp main panel outdoors holding those high amp breakers including one feeding this interior sub panel. Beats me, but I can tell you how I did mine...
The high amp breakers for electric heat, a/c, range, dryer, interior subpanel are in the outdoor/exterior panel. Basement lighting, etc.. is from my interior subpanel just like yours.
Two additional 220 feeds to my basement were pulled from the exterior main panel. My interior subpanel might have handled the addition of one 30 amp 220 line but I wasn't willing to try.
See pic, the gray rectangle box in that tail pipe is where the 2 added lines enter the crawl space portion and go on to the basement portion. The RV box was added last summer
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