What sort of workflow is this? From what you stated, work is done on the local PC and only saved to the NAS for backups?
You're not actively working off the NAS?

How many clients are we talking about? What sort of PCs? What networking backbone do you have?

Working off the NAS ie. your active files live on the NAS will require more NAS resources compared to just backing up to NAS
More clients, more higher end PCs, 10Gbit networking = high end NAS with more RAM and spindles

Finally how important is the data on the NAS? Remember RAID or mirroring is not the same as backups.
If you get a ransomware, then everything on your RAID will be encrypted as well.

If you're just one person and have a lot of work stuff on your PC and only need a backup solution then a NAS is nice to have but probably overkill.

Synology and Qnap make some excellent NAS systems for home/SOHO use. You can start there.

Haha so which one is the setup? One person or 5 people? How much data are we talking about roughly?
Backups is a different use case and is only one capability that a NAS can do.

The steps below works if your objective is for backups. Cloud would be for disaster recovery and is optional but highly recommended for you.

If one person:

1. get an external USB drive
2. install Veeam free, backup from one PC to that external drive
3. buy some cloud backup for offsite. Veeam can backup to cloud as well. Backblaze is cheapest but if your data is not a lot there are other cheaper options eg. Onedrive

If 5 people (or is it 1 person with 5 PCs?) backing up to NAS

1. make sure you have a wired network. NAS can work with wifi but it'll be slower
2. buy NAS
3. install Veeam free, backup from PCs to NAS
3b. or if you don't want to spend the money, buy one USB drive, setup one PC as the Veeam backup server to backup other PCs
4. buy cloud backup, sync from NAS to cloud. Qnap, Synology, etc all can backup to cloud