ok
for so small company and that small user quantity, you can run everything in the same box, lets see
you can purchase a new server with 32-64 RAM, one or two processors (2.2 or faster, remember, is better to purchase the sever for at least 5 years so you need 2 processors), 4 hard disks 500 gb or more in RAID 10
install your windows server 2016 or newer
if you want to use windows logins you need to raise the server to domain level, or if you have a domain, use that one.
if you want to use UserPassword, you dont need a domain (i prefer a domain, always)
once you finished you windows setup (windows, domain, dns, iis) you need to install your SQL Server (2014 or better) if you have a license for that
if you dont have any SQL license, you can use the little sql that comes in the BC Setup
once you finished the SQL setup then you can run your BC setup and install the full components (BC Server, Web server, Database and help server)
add your users to BC (windows users or UserName in BC)
So, if you see, you dont need to bought more than one server and you dont need an active directory (i have a laptop with windows server, SQL and NAV 2009 to 2018 and BC wave 2 running without problems, Icore7, 16 ram and 1 TB hdd)
