Creating a Mesh Network with Dell Powerconnect Switches

I am re-designing a network that currently is configured as a Hub-Spoke. To simplify the network, I drafted an extremely sloppy paint diagram to simplify my question. I do have Visio's but am not comfortable sharing them online.

All Switches are Powerconnect N3000 series.
I have 2 switches in a stack via stacking cable.
3 other switches are in separate buildings. As it stands, each of these three switches connects back to the core stack via LAG.
There LAGs consist of two 1GB interfaces on a distant switch, connecting to the LAG on the Core stack (split between 1/0/X and 2/0/X).
I would like to make this a mesh network, so I would like to connect each of the distant switches to each other so that they can still communicate if a link to the core switch goes down.
For example, Distant SW1 link to Core goes down, I would like packets to take path of SW2 to Core.

I tried to make this as simple as possible for sake of the question. So, I am wondering what needs to be programmed on the switches for this to work. I know STP is enabled by default, but I believe this is a global config. Do I need to do any further configurations, or simply connect the distant switches together and configure the interfaces as Trunks?

Thanks in advance.