If you’re just putting links on the page to the recording (as per Sean’s example and my suggestion) you won’t be slowing the page down discernably – a few extra bytes for the link which no-one will notice.
The links Sean puts in just play in your browser. Or you can right click & save the file to play elsewhere. Same would happen with S3 hosting and I guess that the other options you’re exploring would give the opportunity to save files locally as well.
Siteground looks like a decent enough host and I’m sure if you get close to any limits they’ll happily sell you an upgrade.
Often it’s a case of ready, fire, aim. Adjust once you find out what’s happening rather than running through all those scary “what ifs” 🙂