Selfhosted

Hi. Some friends of mine are starting a business and they want to setup a server to host a simple "contact" website, run an e-mail service (about 10 accounts for now but with possibilities of expanding it to support more) and to store and remote access documents.

Im a computer savvy person so they asked me for help, but dont know much about self-hosting so I come here asking you:

What kind of hardware do they need and would be best? What OS and other software is required and recomended?
How to set it up/configure it? Im partial to foss but if there are good propietary options they are acceptable too. And last: What do we have to watch out for or avoid.

Also, space is a bit of an issue, I was thinking they could use something small like an intel nuc but Im worried that hardware would be underpowered for their needs.

I have been googling for stuff myself but I get overwhelmed by the ammount of information and some contradicting opinions so I appreciate your recomendations and guidance. Im not asking you to give me a full tutorial, although I would appreciate it too, but just to be pointed in the right direction to avoid, as much as possible, spending money and time on things they might not really need or might not perform as well.

Thanks in advance.