G3 3500 ssd is full

My G3 is about a year old. It has 8gb ram, 1 m.2 256mb and the open spot for a 2.5”  sata  ssd. Adding the 2.5 should be the easy button, but I would like to replace the m.2 with a 1Tb stick to keep the speed. I would also, in the future like to dual boot Linux too from the m.2. 

I understand that I would need to clone the 256 on to the 1Tb with 3rd party software and there can be problems booting from usb. 

I’m looking for input from people that know more than me. 

Thanks Markinwi