Following in the footsteps of what I would call its big brother, the H440, building in the S340 was seamlessly easy and took no time at all. This is in big part due to the fact that the entire power supply is hidden so no need to worry about all those horrid cables. As you can see in the picture below the only cables on show from the power supply are the 24pin CPU and the 8+6 pin GPU power cables and even then it is at a minimum of what is visible due to the unique white bar that covers the hole that allows for cables to come from the bottom compartment to be plugged into the motherboard and components.
While I did not install a radiator in the front of the case, I did install the Corsair H80i in the rear of the case and there was plenty of room to do so. Looking at the picture it does look a bit close to the top exhaust fan but this did not cause any problems while installing the H80i or even after when using it.
The only real thing to mention about installing hardware into the S340 is when it comes to installing the power supply. While part of it is just me being very lazy, you cannot just slot most power supplies in and screw them to the case. There is a little face plate that will you need to take off so you can slot the power supply in from the rear, put the faceplate back on and then screw the power supply to it. It only takes an extra 10 seconds or so to do this and is really not an issue, just something to be aware of.