Please don't use OwnCloud. It eats your files and cost us loads of time and effort, in addition to sowing FUD among my office coworkers, who thought someone was deleting files from the shared/sync drive. Plus it doesn't support delta sync [0], so if (for example) you're syncing large files like (for example) True/VeraCrypt volumes, you're going to be pushing a lot of data around. This is especially awful since you're not doing this on a LAN but to S3, which means your raw cost in dollars for operating this software will be much much larger than with another solution like SyncThing or Seafile which does support delta sync.

[0] https://owncloud.org/faq/#partialsyncing