MikroTik

I currently have my whole backhaul in one subnet, I don't believe this is ideal for the future. I'm also having trouble grasping how to set the same subnet across multiple ethers, I don't see the light.

My questions are:

Should I rather have each tower in their own subnet?

Please advise how to set the same subnet across multiple ethers.

Thank you.

What you would like to achieve is called a bridged network.
You need to create a bridge, add all the interfaces that you are using to connect your backhaul into the bridge and assign an IP address to the bridge interface (not any ethernet or wlan interfaces!).
As you already said in your post this is not an ideal network design and doesn't scale well, but it is the easiest one.
To study up on networking basics go here:

http://wiki.mikrotik.com/wiki/Testwiki

Once you have a better understanding of how networking works you can convert to a routed network and assign individual subnets to each link and let OSPF do the routing for you.