I had a 4 bay Synology at the start, then switched to HP microserver because it was much more powerful in terms of hardware and in theory it can do much more. But then decided it was too noisy, wasteful on energy and way too much configuration. Now I run a 2 bay Synology on 24/7 with periodic non-destructive backup script (like TimeMachine but using Rsync) to the HP microserver.
4 bay is nice, but if you want it on 24/7, I don't think 4 bay is the answer. Are you wanting RAID for always-running reliability or want it as a backup? RAID is not backup! If you run single disks with external backup disks, you can power-off or disconnect external disks and not suffer file losses in case of virus or accidental delete. It's really easy to retrieve a backup, only downside is you will have some down-time to your server compared to RAID.