Having two different RAID configurations in a NAS

I am in the process of buying a new NAS and I am putting down some requirements in order to decide which brand / model suits me better.

Generally I can say that I am using two 'types' of files everyday

1. Some Very important files for which I need some replication / redundancy. Those are a lot small, document (in the majority) and image files.
2. Some large files in size, which I do not care if I lose and they are easily replaceable. These files are raw data, export or rip, which I use temporally but I want to 'share' them, and that why I want them on NAS.

I am thinking of buying a 4bay NAS and

• Configure the 3 slots (2TB or 3TB disks) in raid 5, to store the first 'type' or my files.
• Use the 4th slot as a single drive (6TB possible), to store the less important second 'type' of files.

Can a NAS configured this way? Are there any special hardware / Software requirements that a NAS should have?

Note 1: Related to Two Raid-1 arrays in a single system?
Note 2: This question is not to argue, which Raid configuration is better and why I am not putting everything in Raid 5/ 6 etc.