But, you still can use smth like Synology cloud sync to synchronize the data on cloud and access them via the internet. For sure, suitable Synology NAS is required.
Most do, yes but best to have at least a passing knowledge in security practices before doing that. At the very least, ensure that whatever you get supports 2FA for user logins and has a track record of patching vulnerabilities quickly. IMO, I wouldn't trust a WD device after their massive hack that killed their service for 10 days.