Not sure that's the right number - I worked in a Mac shop (an engineering firm) with 20-30 users with 21" iMacs, served off a single Mac Mini server. If your users are just normal users, iMacs are fine. (Though the Macs did come under fire from the finance folks - taking the line that "equivalent" PCs are "industry standard" and a third of the price. I think this argument won out in the end, and the Macs all disappeared one day. It's a shame).

Of course, the finance folks all have Windows laptops that cost the same as Apple laptops, "because we're finance".

but 2tb is just to small and id want to use esxi to virtualise the server we have tools that run on Ubuntu

Why not use USB-3 storage?

Its another box to buy and manage