Spec me a NAS for my small business

Hello experts. Hoping someone can help me out.

I run a small construction business and want to set up file sharing between computers. This will serve as file back up as well. Due to the nature of the business, most employees are out in the field, but I have around 25 people full time in the office. These 25 have their own computers/laptops connected to the internet either by ethernet or wifi.

Here is how i want the setup to be:

All the documents they generate daily or weekly will be transferred to the NAS, to a certain folder which I will have access to anytime, even when im out of the office or abroad.

I want the files they put in to be "locked". Meaning they wont be able to delete or make changes to the files. If they want to update a certain file/document they they can simply upload the new one. I will be the master controller of the files if that makes sense. 2TB of storage is enough to start with (4TB in Raid 1), with future upgrade-ability in mind.

I am techy in some ways but new to networking and the like. Looking for something easy to set up and forget about. Googling around I am choosing between: Western Digital My Cloud DL2100 or the Seagate NAS PRO 2bay.

Comments anyone?

With that amount of employees I have to ask the question is a NAS enough? If you don't want the upfront cost of a full blown server and domain then I would suggest some kind of cloud based storage and platform such as Office 365 with SharePoint which will allow you to handle documents, versions of documents and so on. This would also work well for field remote workers. This option would take longer to setup however and will be the more costly route.

I would only advise a NAS to a small company with less than 10 workers at most if they didn't care about permissions and so on.

Seagate's NAS is advertised to cater up to <50 users. Not sure how this would translate to real world use though.

I checked the base offering of Office 365 and I think its a pretty good deal at $5/user/month. However, that permits the use of office online only.. or we could keep using our old ms office. Also we are not limited to using office apps alone.

Google also has a similar model "google apps for work" that is $5/user/month. I guess I would have to weigh the pros and cons of having a cloud platform as our file sharing and backup.

One major pro, your backups are offsite.

If your NAS is intended to be your file store, DO NOT USE IT FOR BACKUPS.

Good point paradigm. I did not think about file security and safety. Now really leaning towards cloud storage