This is a really nice NAS. I have the DS723+ which is the 2 bay version. Lots of functionality!
I suggest you check out https://www.synology.com/en-us/support/RAID_calculator if you haven't already purchased hard drives yet. It'll help you determine what type of raid to use based on the size and number of drives you have. It is not always better to have more drives of mixed capacity due to the way the redundancy calculates available space.
Also check out this site if you're looking for good price on recertified drives
I have a pair of Seagate exos x18 that are not too loud, have tons of capacity, and haven't let me down at all.