Certain subtitle formats cannot be directly streamed, so your server is probably re-encoding video on the fly to burn in the subtitles. PGS format is actually a series of images and will always require re-encoding video. Picking SRT should work with device direct streaming.
Highly recommend. I moved my web hosting from my home server to a CPX11 server for better uptime (my tinkering around in the homelab was always bringing things down) and couldn’t be happier. It’s dirt cheap (cheaper than shared web hosting, even), performant (performance is better than shared web hosting) and reliable. With a 20TB bandwidth limit at the lowest tier, I can reverse proxy for most of my homelab, too.
It can save data by excluding data streams that you don’t need. For instance, I don’t need French, Italian, Japanese, German 5.1 audio streams that each have 700Mbps bitrates or higher, nor do I need an English 1.5Gbps master audio stream, a 700 Mbps English stream, a 500 Mbps descriptive audio for the blind, and 5 different special edition commentary tracks for a film I’ll watch once or twice. All those tracks can really add up, and torrent sites are often country or language specific, so remuxes might have original language and/or native language audio only.
I don’t know what you mean by “ethical”, but I use Sendgrid. They have a free tier that can send up to 100 emails a day.