Help with small wired network?

Question

My office has 7 iMacs and 3 MacBooks using ethernet cables to connect via a hub. I'm trying to establish a wired network between these, so as to allow full browsing and read/write access among them while preventing access to any computer not physically connected.
I understand I can set the home folders to shared, but a few problems present:
1. This seems to establish wireless sharing, whereas we need a wired-only network.
2. I understand how to share between accounts on a single computer, say, accounts A and B on computer X. But how to add permissions for accounts on other computers (e.g. account Y on computer Z)?

Answer 1

Yep, I realize that, and it's where I'm stuck at. I'm only seeing two possibilities, neither of which is helpful...
A. allow permissions for "Users & Groups" on the same computer, which ignores the goal of networking users from other computers.
B. allow "Everyone" with a wireless connection, which ignores the goal of creating a network between only the office computers.
So the Receptionist computer wants to allow access to users from the Front Office computer, Technicians computer, and Back Office computer. Back office wants to allow users from the Technicians computer, Front Office computer, and so forth.
But for example, all I can figure out now is how to allow users on the Receptionist computer to allow other users on the Receptionist computer, or else to allow all users from any computer with a wireless connection...