Mmkay, so what were my core mistakes? Unit conversion failures? Order-of-magnitude errors? Sign problems (somehow)?

Both Wolfram Alpha and units(1) indicated that conversion between MW and MWh was totally nonsensical, so I presumed either that that was a typo, or that 1MW of power generation run for one hour will satisfy 1MWh of demand... assuming that either that demand is evenly spread throughout the hour, or that you can smooth over spikes with storage.

Your mistake is ignoring capacity factor. Most power generation has between 40% and 60% capacity factor. NPPs are 90+ and renewables are about 10. This is intentionally made confusing and you aren't helping because you don't understand this. I do get that this is a good faith error caused by the intention conflation of different units by PR statements.