I wouldnt say its necessary for a fan in the tower. I have only had issues when its really hot, but 70 F or below and I dont have many issues with foaming. That being said, it is recommended
But I would make it a last priority, get that thing up and running first. Adding a collar to a fridge can be a pain. Might I give you a little advice as I made some mistakes in my build...
When you put the 1 inch support feet on the front of the collar (so it doesn't rip off the fridge), make sure they are inset a little to the inside or you will have no where to mount the door hinge.
I found that my door didnt seal as well as I would like so I put a latch on it that helps make a nice tight seal. Because you no longer have the magnetic connection of the fridge or that nice flat seal for the door it can cause issues with the seal.
And lastly I went to a hardware store and got some double stick soft foam insulation (2 in wide) and put that between the wood and the fridge for a nice tight seal.
Another thing I did, I painted my collar with a paint called Kilz, it stops mold from growing. I figured that since I would be putting beer in this guy and for sure would spill now and then I would be nice to now have to worry about mold, so far it has worked.
Lastly, this one is for starrfish, you can use a fridge with a freezer. Just bring the fridge up to room temp, make sure all the copper piping is at room temp not still frozen and bend the freezer down. As long as everything is warmed up it all bends really easy. The key is to just go slow and make sure you dont kink it. Of course it would be ideal to have one without the freezer they are just a lot harder to find.