The problem with Backblaze is the cheap option is not intended as normal cloud storage, its for backups only and if you need to recover you have to do a FULL recovery, not incremental. It seems to be a last-resort kind of service. You're also not supposed to use it with a NAS, its meant to be for client backups only. (a curious distinction given I backup my clients to the NAS for that purpose and its those backups I'd like to have a secondary backup of)
Cloud storage would also be a pretty horrible way to store my movies/TV shows as part of the reason is to have them local and fully accessibly without using the Internet. Plus who knows if they will start scanning for "high seas" copies in your cloud storage, they're not going to care that I only have that stuff because I can't obtain it any other way in that quality, or stuff I bought but had to obtain DRM free copies.
I'm also not sure your estimates of power consumption is right, given my 8600k server with 50TB of storage, main switch, router, Litebeam, WiFi AP, two monitors for the CCTV, all combined comes out at 135W average according to the UPS. That said I removed my CCTV DVR from the UPS and the consumption isn't showing any different, so there may be some inaccuracy in its measurements (I suspect it rounds up/down by 5W or so and its averaged over a certain time).
Also consider that other than on hot summer days, that electricity usage is being converted to heat. If you reduce your electricity use, some of that will be offset in gas usage if you have gas heating.