New Server for small accounting and bookkeeping business

I own a small business. I have 5 employees in my company. We are a bookkeeping company. I am looking to create a server for my business. Should I build my own server or buy a new one like
I don’t have experience in building or assembling a server is it a difficult task?

The server you linked is a blade. It needs a larger chassis to run in and would not fit your needs.

You should build your own, as well as have a secure/encrypted cloud backup such as Backblaze B2.