How to improve my network with several Enterasys switches?

[soporteciardi]

Hello friends
I recently started working in a company as IT solutions. I found the network in this way.

Central Branch, Router Mitrotik RB1100AHx4-
I have 3 switches connected, 1 on the first floor and 2 on the ground floor.
2 smaller branches connected wireless point-to-point.
I share a scheme that you make to understand it better.

SW 3 is connected to SW 2 by UTP, would it have to connect it by optical fiber? I imagine it improves the transfer.

With the passing of time they were adding devices, now I need to add a swich in the central house, I wonder, what would be the best way?
The new SW 4 thought to connect it to SW 1 by optical fiber, could you give me your opinion is very valuable to me

What topology would be better to use in this case?

Thanks

[AdrianO]

If the switch are in the same rack I would stack them with stacking cables, you can stack up to 8 switches. If they are far apart UTP cat 6 or 6a is fine for 1G speeds (C3 family doesn't support 10G), you dont need fiber unless the distances between switch are greater than ~80-90 meters.